Imperial College London

ProfessorArashMostofi

Faculty of EngineeringDepartment of Materials

Professor of Theory and Simulation of Materials
 
 
 
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Contact

 

+44 (0)20 7594 8154a.mostofi Website

 
 
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Location

 

Bessemer B332Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

97 results found

Aghajanian M, Mostofi AA, Lischner J, 2023, Optical properties of charged defects in monolayer MoS₂, Electronic Structure, Vol: 5, ISSN: 2516-1075

We present theoretical calculations of the optical spectrum of monolayer MoS2 with a charged defect. In particular, we solve the Bethe–Salpeter equation based on an atomistic tight-binding model of the MoS2 electronic structure which allows calculations for large supercells. The defect is modelled as a point charge whose potential is screened by the MoS2 electrons. We find that the defect gives rise to new peaks in the optical spectrum approximately 100–200 meV below the first free exciton peak. These peaks arise from transitions involving in-gap bound states induced by the charged defect. Our findings are in good agreement with experimental measurements.

Journal article

Wang Y, Laihonen S, Unge M, Mostofi Aet al., 2023, The effect of chemistry and thermal fluctuations on charge injection barriers at aluminum/polyolefin interfaces, Journal of Applied Physics, Vol: 134, Pages: 1-9, ISSN: 0021-8979

Charge injection at metal/polymer interfaces is a critical process in many technological devices, including high voltage capacitors and cables in which polyolefin materials, such as polyethylene (PE) and polypropylene (PP), are often used as insulation materials. We use simulations based on density-functional theory to study charge injection at aluminum/PE and aluminum/PP interfaces. Specifically, we investigate the influence of incorporating a variety of polar chemical impurities at the PE and PP chain ends on electron and hole injection barriers. Crucially, we account for the effect of thermal disorder by considering ensembles of thousands of interface structures obtained from ab initio molecular dynamics trajectories at 373 K. We show that the mean injection barrier can change by up to 1.1 eV for Al/PE and 0.6 eV for Al/PP, as compared to the pristine case, depending on which chemical impurity is introduced. We also show that the spread of injection barriers from thermal fluctuations also depends strongly on the chemistry of the impurity. The observed trends can be understood with a simple model based on thermal fluctuations of the dipole moment density associated with the chemical impurity at the interface. We further verify this model by considering larger interface models with lower impurity densities. Our results demonstrate that small chemical modifications, which may arise from oxidation, for example, have a significant influence on charge injection barriers in metal/polyolefin interfaces.

Journal article

Tepliakov NV, Ma R, Lischner J, Kaxiras E, Mostofi AA, Pizzochero Met al., 2023, Dirac half-semimetallicity and antiferromagnetism in graphene nanoribbon/Hexagonal boron nitride heterojunctions, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 23, Pages: 6698-6704, ISSN: 1530-6984

Half-metals have been envisioned as active components in spintronic devices by virtue of their completely spin-polarized electrical currents. Actual materials hosting half-metallic phases, however, remain scarce. Here, we predict that recently fabricated heterojunctions of zigzag nanoribbons embedded in two-dimensional hexagonal boron nitride are half-semimetallic, featuring fully spin-polarized Dirac points at the Fermi level. The half-semimetallicity originates from the transfer of charges from hexagonal boron nitride to the embedded graphene nanoribbon. These charges give rise to opposite energy shifts of the states residing at the two edges, while preserving their intrinsic antiferromagnetic exchange coupling. Upon doping, an antiferromagnetic-to-ferrimagnetic phase transition occurs in these heterojunctions, with the sign of the excess charge controlling the spatial localization of the net magnetic moments. Our findings demonstrate that such heterojunctions realize tunable one-dimensional conducting channels of spin-polarized Dirac fermions seamlessly integrated into a two-dimensional insulator, thus holding promise for the development of carbon-based spintronics.

Journal article

Ramzan MS, Goodwin ZAH, Mostofi AA, Kuc A, Lischner Jet al., 2023, Effect of Coulomb impurities on the electronic structure of magic angle twisted bilayer graphene, npj 2D Materials and Applications, Vol: 7, Pages: 1-8, ISSN: 2397-7132

In graphene, charged defects break the electron-hole symmetry and can evengive rise to exotic collapse states when the defect charge exceeds a criticalvalue which is proportional to the Fermi velocity. In this work, we investigatethe electronic properties of twisted bilayer graphene (tBLG) with chargeddefects using tight-binding calculations. Like monolayer graphene, tBLGexhibits linear bands near the Fermi level but with a dramatically reducedFermi velocity near the magic angle (approximately 1.1{\deg}). This suggeststhat the critical value of the defect charge in magic-angle tBLG should also bevery small. We find that charged defects give rise to significant changes inthe low-energy electronic structure of tBLG. Depending on the defect positionin the moir\'e unit cell, it is possible to open a band gap or to induce anadditional flattening of the low-energy valence and conduction bands. Ourcalculations suggest that the collapse states of the two monolayers hybridizein the twisted bilayer. However, their in-plane localization remains largelyunaffected by the presence of the additional twisted layer because of thedifferent length scales of the moir\'e lattice and the monolayer collapse statewavefunctions. These predictions can be tested in scanning tunnellingspectroscopy experiments.

Journal article

Maity I, Mostofi AA, Lischner J, 2023, Electrons surf phason waves in moiré bilayers, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 23, Pages: 4870-4875, ISSN: 1530-6984

We investigate the effect of thermal fluctuations on the atomic and electronic structure of a twisted MoSe2/WSe2 heterobilayer using a combination of classical molecular dynamics and ab initio density functional theory calculations. Our calculations reveal that thermally excited phason modes give rise to an almost rigid motion of the moiré lattice. Electrons and holes in low-energy states are localized in specific stacking regions of the moiré unit cell and follow the thermal motion of these regions. In other words, charge carriers surf phason waves that are excited at finite temperatures. We also show that such surfing survives in the presence of a substrate and frozen potential. This effect has potential implications for the design of charge and exciton transport devices based on moiré materials.

Journal article

Tepliakov NV, Lischner J, Kaxiras E, Mostofi AA, Pizzochero Met al., 2023, Unveiling and manipulating hidden symmetries in graphene nanoribbons, Physical Review Letters, Vol: 130, Pages: 1-6, ISSN: 0031-9007

Armchair graphene nanoribbons are a highly promising class of semiconductors for all-carbon nanocircuitry. Here, we present a new perspective on their electronic structure from simple model Hamiltonians and ab initio calculations. We focus on a specific set of nanoribbons of width n=3p+2, where n is the number of carbon atoms across the nanoribbon axis and p is a positive integer. We demonstrate that the energy-gap opening in these nanoribbons originates from the breaking of a previously unidentified hidden symmetry by long-ranged hopping of π electrons and structural distortions occurring at the edges. This hidden symmetry can be restored or manipulated through the application of in-plane lattice strain, which enables continuous energy-gap tuning, the emergence of Dirac points at the Fermi level, and topological quantum phase transitions. Our work establishes an original interpretation of the semiconducting character of armchair graphene nanoribbons and offers guidelines for rationally designing their electronic structure.

Journal article

Tidey JP, Keegan C, Bristowe NC, Mostofi AA, Hong Z-M, Chen B-H, Chuang Y-C, Chen W-T, Senn MSet al., 2022, Structural origins of the low-temperature orthorhombic to low-temperature tetragonal phase transition in high-Tc cuprates, Physical Review B, Vol: 106, ISSN: 2469-9950

We undertake a detailed high-resolution diffraction study of a plain band insulator, La2MgO4, whichmay be viewed as a structural surrogate system of the undoped end-member of the high-Tc superconductorfamily La2−x−yA2+x R3+y CuO4 (A = Ba, Sr; R = rare earth). We find that La2MgO4 exhibits the infamous lowtemperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase transition that has been linked to thesuppression of superconductivity in a variety of underdoped cuprates, including the well-known La2−xBaxCuO4(x = 0.125). Furthermore, we find that the LTO-to-LTT phase transition in La2MgO4 occurs for an octahedraltilt angle in the 4◦–5◦ range, similar to that which has previously been identified as a critical tipping pointfor superconductivity in these systems. We show that this phase transition, occurring in a system lackingspin correlations and competing electronic states such as charge density waves and superconductivity, can beunderstood by simply navigating the density functional theory ground-state energy landscape as a function ofthe order parameter amplitude. This result calls for a careful reinvestigation of the origins of the phase transitionsin high-Tc superconductors based on the hole-doped, n = 1 Ruddlesden-Popper lanthanum cuprates.

Journal article

Cheung CTS, Goodwin ZAH, Vitale V, Lischner J, Mostofi AAet al., 2022, Atomistic Hartree theory of twisted double bilayer graphene near the magic angle, Electronic Structure, Vol: 4, Pages: 1-11, ISSN: 2516-1075

Twisted double bilayer graphene (tDBLG) is a moiré material that has recently generated significant interest because of the observation of correlated phases near the magic angle. We carry out atomistic Hartree theory calculations to study the role of electron–electron interactions in the normal state of tDBLG. In contrast to twisted bilayer graphene, we find that such interactions do not result in significant doping-dependent deformations of the electronic band structure of tDBLG. However, interactions play an important role for the electronic structure in the presence of a perpendicular electric field as they screen the external field. Finally, we analyze the contribution of the Hartree potential to the crystal field, i.e. the on-site energy difference between the inner and outer layers. We find that the on-site energy obtained from Hartree theory has the same sign, but a smaller magnitude compared to previous studies in which the on-site energy was determined by fitting tight-binding results to ab initio density-functional theory (DFT) band structures. To understand this quantitative difference, we analyze the ab initio Kohn–Sham potential obtained from DFT and find that a subtle interplay of electron–electron and electron–ion interactions determines the magnitude of the on-site potential.

Journal article

Aghajanian M, Mostofi A, Lischner J, 2022, Electronic structure of monolayer and bilayer black phosphorus with charged defects, Physical Review Materials, Vol: 6, Pages: 1-13, ISSN: 2475-9953

We use an atomistic approach to study the electronic properties of monolayer and bilayer black phosphorus in the vicinity of a charged defect. In particular, we combine screened defect potentials obtained from first-principles linear response theory with large-scale tight-binding simulations to calculate the wave functions and energies of bound acceptor and donor states. As a consequence of the anisotropic band structure, the defect states in these systems form distorted hydrogenic orbitals with a different ordering from that in isotropic materials. For the monolayer, we study the dependence of the binding energies of charged adsorbates on the defect height and the dielectric constant of a substrate in an experimental setup. We also compare our results with an anisotropic effective mass model and find quantitative and qualitative differences when the charged defect is close to the black phosphorus or when the screening from the substrate is weak. For the bilayer, we compare results for charged adsorbates and charged intercalants and find that intercalants induce more prominent secondary peaks in the local density of states because they interact strongly with electronic states on both layers. These insights can be directly tested in scanning tunneling spectroscopy measurements and enable a detailed understanding of the role of Coulomb impurities in electronic devices.

Journal article

Maity I, Mostofi AA, Lischner J, 2022, Chiral valley phonons and flat phonon bands in moire materials, Physical Review B: Condensed Matter and Materials Physics, Vol: 105, Pages: 1-6, ISSN: 1098-0121

We investigate the chirality of phonon modes in twisted bilayer WSe2 and demonstrate distinct chiral behavior of the K/K′ valley phonons for twist angles close to 0∘ and close to 60∘. In particular, multiple chiral nondegenerate K/K′ valley phonons are found for twist angles near 60∘ whereas no nondegenerate chiral modes are found for twist angles close to 0∘. Moreover, we discover two sets of emergent chiral valley modes that originate from an inversion symmetry breaking at the moiré scale and find similar modes in moiré patterns of strain-engineered bilayers WSe2 and MoSe2/WSe2 heterostructures. At the energy gap between acoustic and optical modes, the formation of flat phonon bands for a broad range of twist angles is observed in twisted bilayer WSe2. Our findings are relevant for understanding electron-phonon and exciton-phonon scattering in moiré materials and also for the design of phononic analogues of flat band electrons.

Journal article

Fischer A, Goodwin ZAH, Mostofi AA, Lischner J, Kennes DM, Klebl Let al., 2022, Unconventional superconductivity in magic-angle twisted trilayer graphene, npj Quantum Materials, Vol: 7, Pages: 1-10, ISSN: 2397-4648

Magic-angle twisted trilayer graphene (MATTG) recently emerged as a highly tunable platform for studying correlated phases of matter, such as correlated insulators and superconductivity. Superconductivity occurs in a range of doping levels that is bounded by van Hove singularities, which stimulates the debate of the origin and nature of superconductivity in this material. In this work, we discuss the role of spin-fluctuations arising from atomic-scale correlations in MATTG for the superconducting state. We show that in a phase diagram as a function of doping (ν) and temperature, nematic superconducting regions are surrounded by ferromagnetic states and that a superconducting dome with Tc ≈ 2 K appears between the integer fillings ν = −2 and ν = −3. Applying a perpendicular electric field enhances superconductivity on the electron-doped side which we relate to changes in the spin-fluctuation spectrum. We show that the nematic unconventional superconductivity leads to pronounced signatures in the local density of states detectable by scanning tunneling spectroscopy measurements.

Journal article

Pizzochero M, Tepliakov N, Mostofi AA, Kaxiras Eet al., 2021, Electrically induced Dirac fermions in graphene nanoribbons, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 9332-9338, ISSN: 1530-6984

Graphene nanoribbons are widely regarded as promising building blocks for next-generation carbon-based devices. A critical issue to their prospective applications is whether their electronic structure can be externally controlled. Here, we combine simple model Hamiltonians with extensive first-principles calculations to investigate the response of armchair graphene nanoribbons to transverse electric fields. Such fields can be achieved either upon laterally gating the nanoribbon or incorporating ambipolar chemical codopants along the edges. We reveal that the field induces a semiconductor-to-semimetal transition with the semimetallic phase featuring zero-energy Dirac fermions that propagate along the armchair edges. The transition occurs at critical fields that scale inversely with the width of the nanoribbons. These findings are universal to group-IV honeycomb lattices, including silicene and germanene nanoribbons, irrespective of the type of edge termination. Overall, our results create new opportunities to electrically engineer Dirac semimetallic phases in otherwise semiconducting graphene-like nanoribbons.

Journal article

Wentink M, Gaberle J, Aghajanian M, Mostofi AA, Curson NJ, Lischner J, Schofield SR, Shluger AL, Kenyon AJet al., 2021, Substitutional tin acceptor states in black phosphorus, The Journal of Physical Chemistry C, Vol: 125, Pages: 22883-22889, ISSN: 1932-7447

Nominally pure black phosphorus (BP) is commonly found to be a p-type semiconductor, suggesting the ubiquitious presence of impurity species or intrinsic, charged defects. Moreover, scanning tunneling microscopy (STM) images of black phosphorus reveal the presence of long-range double-lobed defect features superimposed onto the surface atomic lattice. We show that both the p-type doping of BP and the defect features observed in STM images can be attributed to substitutional tin impurities. We show that black phosphorus samples produced through two common synthesis pathways contain tin impurities, and we demonstrate that the ground state of substitutional tin impurities is negatively charged for a wide range of Fermi level positions within the BP band gap. The localized negative charge of the tin impurities induces hydrogenic states in the band gap, and it is the 2p level that sits at the valence band edge that gives rise to the double-lobed features observed in STM images.

Journal article

Goodwin Z, Klebl L, Vitale V, Liang X, Gogtay V, Gorp XV, Kennes DM, Mostofi AA, Lischner Jet al., 2021, Flat bands, electron interactions and magnetic order in magic-angle mono-trilayer graphene, Physical Review Materials, Vol: 5, ISSN: 2475-9953

Starting with twisted bilayer graphene, graphene-based moiré materials have recently been established as a new platform for studying strong electron correlations. In this paper, we study twisted graphene monolayers on trilayer graphene and demonstrate that this system can host flat bands when the twist angle is close to the magic angle of 1.16∘. When monolayer graphene is twisted on ABA trilayer graphene, the flat bands are not isolated, but are intersected by a Dirac cone with a large Fermi velocity. In contrast, graphene twisted on ABC trilayer graphene (denoted AtABC) exhibits a gap between flat and remote bands. Since ABC trilayer graphene and twisted bilayer graphene are known to host broken-symmetry phases, we further investigate the ostensibly similar magic-angle AtABC system. We study the effect of electron-electron interactions in AtABC using both Hartree theory and an atomic Hubbard theory to calculate the magnetic phase diagram as a function of doping, twist angle, and perpendicular electric field. Our analysis reveals a rich variety of magnetic orderings, including ferromagnetism and ferrimagnetism, and demonstrates that a perpendicular electric field makes AtABC more susceptible to magnetic ordering.

Journal article

Andersen CW, Armiento R, Blokhin E, Conduit GJ, Dwaraknath S, Evans ML, Fekete Á, Gopakumar A, Gražulis S, Merkys A, Mohamed F, Oses C, Pizzi G, Rignanese G-M, Scheidgen M, Talirz L, Toher C, Winston D, Aversa R, Choudhary K, Colinet P, Curtarolo S, Di Stefano D, Draxl C, Er S, Esters M, Fornari M, Giantomassi M, Govoni M, Hautier G, Hegde V, Horton MK, Huck P, Huhs G, Hummelshøj J, Kariryaa A, Kozinsky B, Kumbhar S, Liu M, Marzari N, Morris AJ, Mostofi AA, Persson KA, Petretto G, Purcell T, Ricci F, Rose F, Scheffler M, Speckhard D, Uhrin M, Vaitkus A, Villars P, Waroquiers D, Wolverton C, Wu M, Yang Xet al., 2021, OPTIMADE, an API for exchanging materials data, Scientific Data, Vol: 8, ISSN: 2052-4463

The Open Databases Integration for Materials Design (OPTIMADE) consortium has designed a universal applicationprogramming interface (API) to make materials databases accessible and interoperable. We outline the first stablerelease of the specification, v1.0, which is already supported by many leading databases and several softwarepackages. We illustrate the advantages of the OPTIMADE API through worked examples on each of the publicmaterials databases that support the full API specification.

Journal article

Prentice J, Mostofi AA, 2021, Accurate and efficient computation of optical absorption spectra of molecular crystals: the case of the polymorphs of ROY, Journal of Chemical Theory and Computation, Vol: 17, Pages: 5214-5224, ISSN: 1549-9618

When calculating the optical absorption spectra of molecular crystals from first principles, the influence of the crystalline environment on the excitations is of significant importance. For such systems, however, methods to describe the excitations accurately can be computationally prohibitive due to the relatively large system sizes involved. In this work, we demonstrate a method that allows optical absorption spectra to be computed both efficiently and at high accuracy. Our approach is based on the spectral warping method successfully applied to molecules in solvent. It involves calculating the absorption spectrum of a supercell of the full molecular crystal using semi-local time-dependent density functional theory (TDDFT), before warping the spectrum using a transformation derived from smaller-scale semi-local and hybrid TDDFT calculations on isolated dimers. We demonstrate the power of this method on three polymorphs of the well-known color polymorphic compound ROY and find that it outperforms both small-scale hybrid TDDFT dimer calculations and large-scale semi-local TDDFT supercell calculations, when compared to the experiment.

Journal article

Vitale V, Atalar K, Mostofi AA, Lischner Jet al., 2021, Flat band properties of twisted transition metal dichalcogenide homo- andheterobilayers of MoS2, MoSe2, WS2 and WSe2, 2D Materials, Vol: 8, ISSN: 2053-1583

Twisted bilayers of two-dimensional materials, such as twisted bilayergraphene, often feature flat electronic bands that enable the observation ofelectron correlation effects. In this work, we study the electronic structureof twisted transition metal dichalcogenide (TMD) homo- and heterobilayers thatare obtained by combining MoS$_2$, WS$_2$, MoSe$_2$ and WSe$_2$ monolayers, andshow how flat band properties depend on the chemical composition of the bilayeras well as its twist angle. We determine the relaxed atomic structure of thetwisted bilayers using classical force fields and calculate the electronic bandstructure using a tight-binding model parametrized from first-principlesdensity-functional theory. We find that the highest valence bands in thesesystems can derive either from $\Gamma$-point or $K$/$K'$-point states of theconstituent monolayers. For homobilayers, the two highest valence bands arecomposed of monolayer $\Gamma$-point states, exhibit a graphene-like dispersionand become flat as the twist angle is reduced. The situation is morecomplicated for heterobilayers where the ordering of $\Gamma$-derived and$K$/$K'$-derived states depends both on the material composition and also thetwist angle. In all systems, qualitatively different band structures areobtained when atomic relaxations are neglected.

Journal article

Klebl L, Goodwin Z, Mostofi AA, Kennes DM, Lischner Jet al., 2021, Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene, Physical Review B, Vol: 103, Pages: 1-7, ISSN: 2469-9950

Electron-electron interactions are intrinsically long ranged, but many models of strongly interacting electrons only take short-ranged interactions into account. Here, we present results of atomistic calculations including both long-ranged and short-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene and demonstrate that qualitatively different results are obtained when long-ranged interactions are neglected. In particular, we use Hartree theory augmented with Hubbard interactions and calculate the interacting spin susceptibility at a range of doping levels and twist angles near the first magic angle to identify the dominant magnetic instabilities. At the magic angle, mostly antiferromagnetic order is found, while ferromagnetism dominates at other twist angles. Moreover, long-ranged interactions significantly increase the twist angle window in which strong correlation phenomena can be expected. These findings are in good agreement with available experimental data.

Journal article

Liang X, Goodwin ZAH, Vitale V, Corsetti F, Mostofi AA, Lischner Jet al., 2020, Effect of bilayer stacking on the atomic and electronic structure of twisted double bilayer graphene, Physical Review B, Vol: 102, Pages: 155146 – 1-155146 – 12, ISSN: 2469-9950

Twisted double bilayer graphene has recently emerged as an interesting moiré material that exhibits strong correlation phenomena that are tunable by an applied electric field. Here we study the atomic and electronic properties of three different graphene double bilayers: double bilayers composed of two AB stacked bilayers (AB/AB), double bilayers composed of two AA stacked bilayers (AA/AA), as well as heterosystems composed of one AB and one AA bilayer (AB/AA). The atomic structure is determined using classical force fields. We find that the inner layers of the double bilayer exhibit significant in-plane and out-of-plane relaxations, similar to twisted bilayer graphene. The relaxations of the outer layers depend on the stacking: atoms in AB bilayers follow the relaxations of the inner layers, while atoms in AA bilayers attempt to avoid higher-energy AA stacking. For the relaxed structures, we calculate the electronic band structures using the tight-binding method. All double bilayers exhibit flat bands at small twist angles, but the shape of the bands depends sensitively on the stacking of the outer layers. To gain further insight, we study the evolution of the band structure as the outer layers are rigidly moved away from the inner layers, while preserving their atomic relaxations. This reveals that the hybridization with the outer layers results in an additional flattening of the inner-layer flat band manifold. Our results establish AA/AA and AB/AA twisted double bilayers as interesting moiré materials with different flat band physics compared to the widely studied AB/AB system.

Journal article

Goodwin Z, Vitale V, Liang X, Mostofi AA, Lischner Jet al., 2020, Hartree theory calculations of quasiparticle properties in twisted bilayer graphene, Physical Review B: Condensed Matter and Materials Physics, Vol: 2, ISSN: 1098-0121

A detailed understanding of interacting electrons in twisted bilayer graphene(tBLG) near the magic angle is required to gain insights into the physicalorigin of the observed broken symmetry phases including correlated insulatorstates and superconductivity. Here, we present extensive atomistic Hartreetheory calculations of the electronic properties of tBLG in the (semi-)metallicphase as function of doping and twist angle. Specifically, we calculatequasiparticle properties, such as the band structure, density of states (DOS)and local density of states (LDOS), which are directly accessible inphotoemission and tunnelling spectroscopy experiments. We find thatquasiparticle properties change significantly upon doping - an effect which isnot captured by tight-binding theory. In particular, we observe that thepartially occupied bands flatten significantly which enhances the density ofstates at the Fermi level and explains the experimentally observed Fermi levelpinning. We predict a clear signature of this band flattening in the LDOS inthe AB/BA regions of tBLG which can be tested in scanning tunnelingexperiments. We also study the dependence of quasiparticle properties on thedielectric environment of tBLG and discover that these properties aresurprisingly robust as a consequence of the strong internal screening. Finally,we present a simple analytical expression for the Hartree potential whichenables the determination of quasiparticle properties without the need forself-consistent calculations.

Journal article

Skylaris C-K, Haynes PD, Mostofi AA, Payne MCet al., 2020, Recent progress in linear-scaling density functional calculations with plane waves and pseudopotentials: the ONETEP code (vol 20, 064209, 2008), JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 32, ISSN: 0953-8984

Journal article

Skylaris C-K, Haynes PD, Mostofi AA, Payne MCet al., 2020, Using ONETEP for accurate and efficient <i>O</i>(<i>N</i>) density functional calculations (vol 17, 175757, 2005), JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 32, ISSN: 0953-8984

Journal article

Haynes PD, Skylaris C-K, Mostofi AA, Payne MCet al., 2020, Density kernel optimization in the ONETEP code (vol 20, 294207, 2008), JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 32, ISSN: 0953-8984

Journal article

Oliveira MJT, Papior N, Pouillon Y, Blum V, Artacho E, Caliste D, Corsetti F, Gironcoli SD, Elena AM, Garcia A, Garcia-Suarez VM, Genovese L, Huhn WP, Huhs G, Kokott S, Kucukbenli E, Larsen AH, Lazzaro A, Lebedeva IV, Li Y, Lopez-Duran D, Lopez-Tarifa P, Luders M, Marques MAL, Minar J, Mohr S, Mostofi AA, O'Cais A, Payne MC, Ruh T, Smith DGA, Soler JM, Strubbe DA, Tancogne-Dejean N, Tildesley D, Torrent M, Yu VW-Zet al., 2020, The CECAM Electronic Structure Library and the modular software development paradigm, Journal of Chemical Physics, Vol: 153, Pages: 024117-1-024117-23, ISSN: 0021-9606

First-principles electronic structure calculations are very widely usedthanks to the many successful software packages available. Their traditionalcoding paradigm is monolithic, i.e., regardless of how modular its internalstructure may be, the code is built independently from others, from thecompiler up, with the exception of linear-algebra and message-passinglibraries. This model has been quite successful for decades. The rapid progressin methodology, however, has resulted in an ever increasing complexity of thoseprograms, which implies a growing amount of replication in coding and in therecurrent re-engineering needed to adapt to evolving hardware architecture. TheElectronic Structure Library (\esl) was initiated by CECAM (European Centre forAtomic and Molecular Calculations) to catalyze a paradigm shift away from themonolithic model and promote modularization, with the ambition to extractcommon tasks from electronic structure programs and redesign them as free,open-source libraries. They include ``heavy-duty'' ones with a high degree ofparallelisation, and potential for adaptation to novel hardware within them,thereby separating the sophisticated computer science aspects of performanceoptimization and re-engineering from the computational science done byscientists when implementing new ideas. It is a community effort, undertaken bydevelopers of various successful codes, now facing the challenges arising inthe new model. This modular paradigm will improve overall coding efficiency andenable specialists (computer scientists or computational scientists) to usetheir skills more effectively. It will lead to a more sustainable and dynamicevolution of software as well as lower barriers to entry for new developers.

Journal article

Pomiro F, Ablitt C, Bristowe NC, Mostofi AA, Won C, Cheong S-W, Senn MSet al., 2020, From first- to second-order phase transitions in hybrid improper ferroelectrics through entropy stabilization, Physical Review B, Vol: 102, Pages: 014101 – 1-014101 – 8, ISSN: 2469-9950

Hybrid improper ferroelectrics (HIFs) have been studied intensively over the past few years to gain an understanding of their temperature-induced phase transitions and ferroelectric switching pathways. Here we report a switching from a first- to a second-order phase transition pathway for HIFs Ca3−xSrxTi2O7, which is driven by the differing entropies of the phases that we identify as being associated with the dynamic motion of octahedral tilts and rotations. A greater understanding of the transition pathways in this class of layered perovskites, which host many physical properties that are coupled to specific symmetries and octahedral rotation and tilt distortions—such as superconductivity, negative thermal expansion, fast ion conductivity, ferroelectricity, among others—is a crucial step in creating novel functional materials by design.

Journal article

Mostofi AA, Skylaris C-K, Haynes PD, Payne MCet al., 2020, "Total-energy calculations on a real space grid with localised functions and a plane-wave basis (vol 147, pg 788, 2002), COMPUTER PHYSICS COMMUNICATIONS, Vol: 252, ISSN: 0010-4655

Journal article

Gołębiowski JR, Kermode JR, Haynes PD, Mostofi AAet al., 2020, Correction: Atomistic QM/MM simulations of the strength of covalent interfaces in carbon nanotube-polymer composites., Physical Chemistry Chemical Physics, Vol: 22, Pages: 14375-14375, ISSN: 1463-9076

Correction for 'Atomistic QM/MM simulations of the strength of covalent interfaces in carbon nanotube-polymer composites' by Jacek R. Gołębiowski et al., Phys. Chem. Chem. Phys., 2020, 22, 12007-12014, DOI: 10.1039/d0cp01841d.

Journal article

Vitale V, Pizzi G, Marrazzo A, Yates J, Marzari N, Mostofi Aet al., 2020, Automated high-throughput Wannierisation, npj Computational Materials, Vol: 6, ISSN: 2057-3960

Maximally-localised Wannier functions (MLWFs) are routinely used to compute from first-principles advanced materials properties that require very dense Brillouin zone integration and to build accurate tight-binding models for scale-bridging simulations. At the same time, high-throughput (HT) computational materials design is an emergent field that promises to accelerate reliable and cost-effective design and optimisation of new materials with target properties. The use of MLWFs in HT workflows has been hampered by the fact that generating MLWFs automatically and robustly without any user intervention and for arbitrary materials is, in general, very challenging. We address this problem directly by proposing a procedure for automatically generating MLWFs for HT frameworks. Our approach is based on the selected columns of the density matrix method and we present the details of its implementation in an AiiDA workflow. We apply our approach to a dataset of 200 bulk crystalline materials that span a wide structural and chemical space. We assess the quality of our MLWFs in terms of the accuracy of the band-structure interpolation that they provide as compared to the band-structure obtained via full first-principles calculations. Finally, we provide a downloadable virtual machine that can be used to reproduce the results of this paper, including all first-principles and atomistic simulations as well as the computational workflows.

Journal article

Prentice J, Aarons J, Womack JC, Allen AEA, Andrinopoulos L, Anton L, Bell RA, Bhandari A, Bramley GA, Charlton R, Clements RJ, Cole DJ, Constantinescu G, Corsetti F, Dubois SM-M, Duff KKB, Escartín JM, Greco A, Hill Q, Lee LP, Linscott E, ORegan DD, Phipps MJS, Ratcliff L, Serrano ÁR, Tait EW, Teobaldi G, Vitale V, Yeung N, Zuehlsdorff T, Dziedzic J, Haynes PD, Hine N, Mostofi AA, Payne MC, Skylaris C-Ket al., 2020, The ONETEP linear-scaling density functional theory program, The Journal of Chemical Physics, Vol: 152, Pages: 174111-1-174111-36, ISSN: 0021-9606

We present an overview of the onetep program for linear-scaling density functional theory (DFT) calculations with large basis set (plane-wave) accuracy on parallel computers. The DFT energy is computed from the density matrix, which is constructed from spatially localized orbitals we call Non-orthogonal Generalized Wannier Functions (NGWFs), expressed in terms of periodic sinc (psinc) functions. During the calculation, both the density matrix and the NGWFs are optimized with localization constraints. By taking advantage of localization, onetep is able to perform calculations including thousands of atoms with computational effort, which scales linearly with the number or atoms. The code has a large and diverse range of capabilities, explored in this paper, including different boundary conditions, various exchange–correlation functionals (with and without exact exchange), finite electronic temperature methods for metallic systems, methods for strongly correlated systems, molecular dynamics, vibrational calculations, time-dependent DFT, electronic transport, core loss spectroscopy, implicit solvation, quantum mechanical (QM)/molecular mechanical and QM-in-QM embedding, density of states calculations, distributed multipole analysis, and methods for partitioning charges and interactions between fragments. Calculations with onetep provide unique insights into large and complex systems that require an accurate atomic-level description, ranging from biomolecular to chemical, to materials, and to physical problems, as we show with a small selection of illustrative examples. onetep has always aimed to be at the cutting edge of method and software developments, and it serves as a platform for developing new methods of electronic structure simulation. We therefore conclude by describing some of the challenges and directions for its future developments and applications.

Journal article

Golebiowski J, Kermode J, Haynes P, Mostofi AAet al., 2020, Atomistic QM/MM simulations of the strength of covalent interfaces in carbon nanotube–polymer composites, Physical Chemistry Chemical Physics, Vol: 22, Pages: 12007-12014, ISSN: 1463-9076

We investigate the failure of carbon-nanotube/polymer composites by using a recently-developed hybrid quantum-mechanical/molecular-mechanical (QM/MM) approach to simulate nanotube pull-out from a cross-linked polyethene matrix. Our study focuses on the strength and failure modes of covalently-bonded nanotube–polymer interfaces based on amine, carbene and carboxyl functional groups and a [2+1] cycloaddition. We find that the choice of the functional group linking the polymer matrix to the nanotube determines the effective strength of the interface, which can be increased by up to 50% (up to the limit dictated by the strength of the polymer backbone itself) by choosing groups with higher interfacial binding energy. We rank the functional groups presented in this work based on the strength of the resulting interface and suggest broad guidelines for the rational design of nanotube functionalisation for nanotube–polymer composites.

Journal article

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