Imperial College London

Professor Peter Haynes

Central FacultyOffice of the Provost

Vice-Provost (Education and Student Experience)



p.haynes Website




Professor Emma McCoy +44 (0)20 7594 8807




409Faculty BuildingSouth Kensington Campus





Publication Type

79 results found

Wang K, Molteni C, Haynes PD, 2022, Localized soft vibrational modes and coherent structural phase transformations in rutile TiO2 nanoparticles under negative pressure, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 22, ISSN: 1530-6984

We study the effect of size on the vibrational modes and frequencies of nanoparticles, by applying a newly developed, robust, and efficient first-principles-based method that we present in outline. We focus on rutile TiO2, a technologically important material whose bulk exhibits a softening of a transverse acoustic mode close to , which becomes unstable with the application of negative pressure. We demonstrate that, under these conditions, nanoparticles above a critical size exhibit unstable localized modes and we calculate their characteristic localization length and decomposition with respect to bulk phonons. We propose that such localized soft modes could initiate coherent structural phase transformations in small nanoparticles above a critical size.

Journal article

Self CN, Khosla KE, Smith AWR, Sauvage F, Haynes PD, Knolle J, Mintert F, Kim MSet al., 2021, Variational quantum algorithm with information sharing, npj Quantum Information, Vol: 7, ISSN: 2056-6387

We introduce an optimisation method for variational quantum algorithms and experimentally demonstrate a 100-fold improvement in efficiency compared to naive implementations. The effectiveness of our approach is shown by obtaining multi-dimensional energy surfaces for small molecules and a spin model. Our method solves related variational problems in parallel by exploiting the global nature of Bayesian optimisation and sharing information between different optimisers. Parallelisation makes our method ideally suited to the next generation of variational problems with many physical degrees of freedom. This addresses a key challenge in scaling-up quantum algorithms towards demonstrating quantum advantage for problems of real-world interest.

Journal article

Yadegari H, Koronfel MA, Wang K, Thornton DB, Stephens IEL, Molteni C, Haynes PD, Ryan MPet al., 2021, Operando measurement of layer breathing modes in lithiated graphite, ACS Energy Letters, Vol: 6, Pages: 1633-1638, ISSN: 2380-8195

Despite their ubiquitous usage and increasing societal dependence on Li-ion batteries, there remains a lack of detailed empirical evidence of Li intercalation/deintercalation into graphite even though this process dictates the performance, longevity, and safety of the system. Here, we report direct detection and dissociation of specific crystallographic phases in the lithiated graphite, which form through a stepwise staging process. Using operando measurements, LiC18, LiC12, and LiC6 phases are observed via distinct low-frequency Raman features, which are the result of displacement of the graphite lattice by induced local strain. Density functional theory calculations confirm the nature of the Raman-active vibrational modes, to the layer breathing modes (LBMs) of the lithiated graphite. The new findings indicate graphene-like characteristics in the lithiated graphite under the deep charged condition due to the imposed strain by the inserted Li. Moreover, our approach also provides a simple experimental tool to measure induced strain in the graphite structure under full intercalation conditions.

Journal article

Rider MS, Sokolikova M, Hanham SM, Navarro-Cia M, Haynes P, Lee D, Daniele M, Guidi MC, Mattevi C, Lupi S, Giannini Vet al., 2020, Experimental signature of a topological quantum dot, Nanoscale, ISSN: 2040-3364

Topological insulators (TIs) present a neoteric class of materials, whichsupport delocalised, conducting surface states despite an insulating bulk. Dueto their intriguing electronic properties, their optical properties havereceived relatively less attention. Even less well studied is their behaviourin the nanoregime, with most studies thus far focusing on bulk samples - inpart due to the technical challenges of synthesizing TI nanostructures. Westudy topological insulator nanoparticles (TINPs), for which quantum effectsdominate the behaviour of the surface states and quantum confinement results ina discretized Dirac cone, whose energy levels can be tuned with thenanoparticle size. The presence of these discretized energy levels in turnleads to a new electron-mediated phonon-light coupling in the THz range. Wepresent the experimental realisation of Bi$_2$Te$_3$ TINPs and strong evidenceof this new quantum phenomenon, remarkably observed at room temperature. Thissystem can be considered a topological quantum dot, with applications to roomtemperature THz quantum optics and quantum information technologies.

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

Hasan H, Mlkvik P, Haynes PD, Vorontsov VAet al., 2020, Generalised stacking fault energy of Ni-Al and Co -Al -W superalloys: Density-functional theory calculations, MATERIALIA, Vol: 9, ISSN: 2589-1529

Journal article

Prentice J, Charlton R, Mostofi AA, Haynes Pet al., 2019, Combining embedded mean-field theory with linear-scaling density-functional theory, Journal of Chemical Theory and Computation, Vol: 16, Pages: 354-365, ISSN: 1549-9618

We demonstrate the capability of embedded mean field theory (EMFT) within the linear-scaling density-functional theory code ONETEP, which enables DFT-in-DFT quantum embedding calculations on systems containing thousands of atoms at a fraction of the cost of a full calculation. We perform simulations on a wide range of systems from molecules to complex nanostructures to demonstrate the performance of our implementation with respect to accuracy and efficiency. This work paves the way for the application of this class of quantum embedding method to large-scale systems that are beyond the reach of existing implementations.

Journal article

Warwick AR, Iniguez J, Haynes PD, Bristowe NCet al., 2019, First-principles study of ferroelastic twins in halide perovskites, Journal of Physical Chemistry Letters, Vol: 10, Pages: 1416-1421, ISSN: 1948-7185

We present an ab initio simulation of 90° ferroelastic twins that were recently observed in methylammonium lead iodide. There are two inequivalent types of 90° walls that we calculate to act as either electron or hole sinks, which leads us to propose a mechanism for enhancing charge carrier separation in photovoltaic devices. Despite separating nonpolar domains, we show these walls to have a substantial in-plane polarization of ∼6 μC cm–2, due in part to flexoelectricity. We suggest this in turn could allow for the photoferroic effect and create efficient pathways for photocurrents within the wall.

Journal article

Golebiowski J, Kermode J, Mostofi A, Haynes Pet al., 2018, Multiscale simulations of critical interfacial failure in carbon nanotube-polymer composites, Journal of Chemical Physics, Vol: 149, ISSN: 0021-9606

Computational investigation of interfacial failure in composite materials is challenging because it is inherently multi-scale: the bond-breaking processes that occur at the covalently bonded interface and initiate failure involve quantum mechanical phenomena, yet the mechanisms by which external stresses are transferred through the matrix occur on length and time scales far in excess of anything that can be simulated quantum mechanically. In this work, we demonstrate and validate an adaptive quantum mechanics (QM)/molecular mechanics simulation method that can be used to address these issues and apply it to study critical failure at a covalently bonded carbon nanotube (CNT)-polymer interface. In this hybrid approach, the majority of the system is simulated with a classical forcefield, while areas of particular interest are identified on-the-fly and atomic forces in those regions are updated based on QM calculations. We demonstrate that the hybrid method results are in excellent agreement with fully QM benchmark simulations and offers qualitative insights missing from classical simulations. We use the hybrid approach to show how the chemical structure at the CNT-polymer interface determines its strength, and we propose candidate chemistries to guide further experimental work in this area.

Journal article

Ratcliff LE, Conduit GJ, Hine NDM, Haynes PDet al., 2018, Band structure interpolation using optimized local orbitals from linear-scaling density functional theory, Physical Review B, Vol: 98, ISSN: 2469-9950

© 2018 American Physical Society. Several approaches to linear-scaling density functional theory (LS-DFT) that seek to achieve accuracy equivalent to plane-wave methods do so by optimizing in situ a set of local orbitals in terms of which the density matrix can be accurately expressed. These local orbitals, which can also accurately represent the canonical Kohn-Sham orbitals, qualitatively resemble the maximally localized Wannier functions employed in band structure interpolation. As LS-DFT methods are increasingly being used in real-world applications demanding accurate band structures, it is natural to question the extent to which these optimized local orbitals can provide sufficient accuracy. In this paper, we present and compare, in principle and in practice, two methods for obtaining band structures. We apply these to a (10, 0) carbon nanotube as an example. By comparing with the results from a traditional plane-wave pseudopotential calculation, the optimized local orbitals are found to provide an excellent description of the occupied bands and some low-lying unoccupied bands, with consistent agreement across the Brillouin zone. However free-electron-like states derived from weakly bound states independent of the σ and π orbitals can only be found if additional local orbitals are included.

Journal article

Charlton RJ, Fogarty R, Bogatko S, Zuehlsdorff TJ, Hine NDM, Heeney MJ, Horsfield AP, Haynes PDet al., 2018, Implicit and explicit host effects on excitons in pentacene derivatives, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606

Anab initiostudy of the effects of implicit and explicit hosts on the excited state properties ofpentacene and its nitrogen-based derivatives has been performed using ground state density func-tional theory (DFT), time-dependent DFT and ∆SCF. We observe a significant solvatochromicredshift in the excitation energy of the lowest singlet state (S1) of pentacene from inclusion inap-terphenyl host compared to vacuum; for an explicit host consisting of six nearest neighbourp-terphenyls, we obtain a redshift of 65 meV while a conductor-like polarisable continuum model(CPCM) yields a 78 meV redshift. Comparison is made between the excitonic properties of pen-tacene and four of its nitrogen-based analogues, 1,8-, 2,9-, 5,12-, and 6,13-diazapentacene with thelatter found to be the most distinct due to local distortions in the ground state electronic struc-ture. We observe that a CPCM is insufficient to fully understand the impact of the host due tothe presence of a mild charge-transfer (CT) coupling between the chromophore and neighbouringp-terphenyls, a phenomenon which can only be captured using an explicit model. The strengthof this CT interaction increases as the nitrogens are brought closer to the central acene ring ofpentacene.

Journal article

Siroki G, Haynes PD, Lee DKK, Giannini Vet al., 2017, Protection of surface states in topological nanoparticles, Physical Review Materials, Vol: 1, ISSN: 2475-9953

opological insulators host protected electronic states at their surface. These states show little sensitivity todisorder. For miniaturization one wants to exploit their robustness at the smallest sizes possible. This is alsobeneficial for optical applications and catalysis, which favor large surface-to-volume ratios. However, it is notknown whether discrete states in particles share the protection of their continuous counterparts in large crystals.Here we study the protection of the states hosted by topological insulator nanoparticles. Using both analyticaland tight-binding simulations, we show that the states benefit from the same level of protection as those on aplanar surface. The results hold for many shapes and sustain surface roughness which may be useful in photonics,spectroscopy, and chemistry. They complement past studies of large crystals—at the other end of possible lengthscales. The protection of the nanoparticles suggests that samples of all intermediate sizes also possess protectedstates.

Journal article

Ready AJ, Haynes PD, Grabowski B, Rugg D, Sutton APet al., 2017, The role of molybdenum in suppressing cold dwell fatigue in titanium alloys, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 473, ISSN: 1364-5021

We test a hypothesis to explain why Ti-6242 is susceptible to cold dwell fatigue, whereas Ti-6246 is not. The hypothesis is that in Ti-6246 substitutional Mo-atoms in $\alpha$-Ti grains trap vacancies thereby limiting creep relaxation. In Ti-6242 this creep relaxation enhances the loading of grains unfavourably oriented for slip and they subsequently fracture. Using density functional theory to calculate formation and binding energies between Mo-atoms and vacancies we find no support for the hypothesis. In the light of this result, and experimental observations of the microstructures in these alloys, we agree with the recent suggestion [J. Qiu, {\it et al.}, Metall. Mater. Trans. A {\bf 45}, 6075 (2014)] that Ti-6246 has a much smaller susceptibility to cold dwell fatigue because it has a smaller grain size and a more homogeneous distribution of grain orientations. We propose that the reduction of the susceptibility to cold dwell fatigue of Ti-6242 at temperatures above about 200~$^\circ$C is due to the activation of $\langle \mathbf{c} + \mathbf{a} \rangle$ slip in `hard' grains, which reduces the loading of grain boundaries.

Journal article

Zuehlsdorff TJ, Haynes PD, Payne MC, Hine NDMet al., 2017, Predicting solvatochromic shifts and colours of a solvated organic dye: the example of nile red, Journal of Chemical Physics, Vol: 146, ISSN: 1089-7690

The solvatochromic shift, as well as the change in colour of the simple organic dye nile red, is studied in two polar and two non-polar solvents in the context of large-scale time-dependent density-functional theory (TDDFT) calculations treating large parts of the solvent environment from first principles. We show that an explicit solvent representation is vital to resolve absorption peak shifts between nile red in n-hexane and toluene, as well as acetone and ethanol. The origin of the failure of implicit solvent models for these solvents is identified as being due to the strong solute-solvent interactions in form of π-stacking and hydrogen bonding in the case of toluene and ethanol. We furthermore demonstrate that the failures of the computationally inexpensive Perdew-Burke-Ernzerhof (PBE) functional in describing some features of the excited state potential energy surface of the S1 state of nile red can be corrected for in a straightforward fashion, relying only on a small number of calculations making use of more sophisticated range-separated hybrid functionals. The resulting solvatochromic shifts and predicted colours are in excellent agreement with experiment, showing the computational approach outlined in this work to yield very robust predictions of optical properties of dyes in solution.

Journal article

Ready AJ, Haynes PD, Rugg D, Sutton APet al., 2017, Stacking faults and the gamma-surface on first-order pyramidal planes in alpha-titanium, Philosophical Magazine, Vol: 97, Pages: 1129-1143, ISSN: 1478-6435

Using first principles methods we calculated the entire gamma-surface of the first-order pyramidal planes in alpha-titanium. Slip on these planes involving dislocations with c+a-type Burgers vectors is one means by which alpha-titanium polycrystals may supplement slip on prism planes with a-type Burgers vectors to maintain ductility. We find one low energy and one high energy stacking fault with energies of 163~mJ/m2 and 681~mJ/m2 respectively. Contrary to previous suggestions we do not find a stable stable stacking fault at (c+a})/2.

Journal article

Corsini NRC, Hine NDM, Haynes PD, Molteni Cet al., 2017, Unravelling the roles of size, ligands and pressure in the piezochromic properties of CdS nanocrystals, Nano Letters, Vol: 17, Pages: 1042-1048, ISSN: 1530-6992

Understanding the effects of pressure-induced deformations on the optoelectronic properties of nanomaterials is important not only from the fundamental point of view but also for potential applications such as stress sensors and electromechanical devices. Here, we describe the novel insights into these piezochromic effects gained from using a linear-scaling density functional theory framework and an electronic enthalpy scheme, which allow us to accurately characterize the electronic structure of CdS nanocrystals with a zincblende-like core of experimentally relevant size. In particular, we focus on unravelling the complex interplay of size and surface (phenyl) ligands with pressure. We show that pressure-induced deformations are not simple isotropic scaling of the original structures and that the change in HOMO–LUMO gap with pressure results from two competing factors: (i) a bulk-like linear increase due to compression, which is offset by (ii) distortions and disorder and, to a lesser extent, orbital hybridization induced by ligands affecting the frontier orbitals. Moreover, we observe that the main peak in the optical absorption spectra is systematically red-shifted or blue-shifted, as pressure is increased up to 5 GPa, depending on the presence or absence of phenyl ligands. These heavily hybridize the frontier orbitals, causing a reduction in overlap and oscillator strength, so that at zero pressure, the lowest energy transition involves deeper hole orbitals than in the case of hydrogen-capped nanocrystals; the application of pressure induces greater delocalization over the whole nanocrystals bringing the frontier hole orbitals into play and resulting in an unexpected red shift for the phenyl-capped nanocrystals, in part caused by distortions. In response to a growing interest in relatively small nanocrystals that can be difficult to accurately characterize with experimental techniques, this work exemplifies the detailed understanding of structure–prop

Journal article

Elliott JD, Poli E, Scivetti I, Ratcliff LE, Andrinopoulos L, Dziedzic J, Hine NDM, Mostofi AA, Skylaris C-K, Haynes PD, Teobaldi Get al., 2016, Chemically selective alternatives to photoferroelectrics for polarization-enhanced photocatalysis: the untapped potential of hybrid inorganic nanotubes, Advanced Science, Vol: 4, ISSN: 2198-3844

Linear-scaling density functional theory simulation of methylated imogolite nanotubes (NTs) elucidates the interplay between wall-polarization, bands separation, charge-transfer excitation, and tunable electrostatics inside and outside the NT-cavity. The results suggest that integration of polarization-enhanced selective photocatalysis and chemical separation into one overall dipole-free material should be possible. Strategies are proposed to increase the NT polarization for maximally enhanced electron–hole separation.

Journal article

Siroki G, Lee DKK, Haynes PD, Giannini Vet al., 2016, Single-electron induced surface plasmons on a topological nanoparticle, Nature Communications, Vol: 7, ISSN: 2041-1723

It is rarely the case that a single electron affects the behaviour of several hundred thousands of atoms. Here we demonstrate a phenomenon where this happens. The key role is played by topological insulators—materials that have surface states protected by time-reversal symmetry. Such states are delocalized over the surface and are immune to its imperfections in contrast to ordinary insulators. For topological insulators, the effects of these surface states will be more strongly pronounced in the case of nanoparticles. Here we show that under the influence of light a single electron in a topologically protected surface state creates a surface charge density similar to a plasmon in a metallic nanoparticle. Such an electron can act as a screening layer, which suppresses absorption inside the particle. In addition, it can couple phonons and light, giving rise to a previously unreported topological particle polariton mode. These effects may be useful in the areas of plasmonics, cavity electrodynamics and quantum information.

Journal article

Tait EW, Ratcliff LE, Payne MC, Haynes PD, Hine NDet al., 2016, Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory, Journal of Physics: Condensed Matter, Vol: 28, ISSN: 1361-648X

Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

Journal article

Zuehlsdorff TJ, Haynes PD, Hanke F, Payne MC, Hine NDet al., 2016, Solvent effects on electronic excitations of an organic chromophore, Journal of Chemical Theory and Computation, Vol: 12, Pages: 1853-1861, ISSN: 1549-9626

In this work we study the solvatochromic shift of a selected low-energy excited state of alizarin in water by using a linear-scaling implementation of large-scale time-dependent density functional theory (TDDFT). While alizarin, a small organic dye, is chosen as a simple example of solute-solvent interactions, the findings presented here have wider ramifications for the realistic modeling of dyes, paints, and pigment-protein complexes. We find that about 380 molecules of explicit water need to be considered in order to yield an accurate representation of the solute-solvent interaction and a reliable solvatochromic shift. By using a novel method of constraining the TDDFT excitation vector, we confirm that the origin of the slow convergence of the solvatochromic shift with system size is due to two different effects. The first factor is a strong redshift of the excitation due to an explicit delocalization of a small fraction of the electron and the hole from the alizarin onto the water, which is mainly confined to within a distance of 7 Å from the alizarin molecule. The second factor can be identified as long-range electrostatic influences of water molecules beyond the 7 Å region on the ground-state properties of alizarin. We also show that these electrostatic influences are not well reproduced by a QM/MM model, suggesting that full QM studies of relatively large systems may be necessary in order to obtain reliable results.

Journal article

Bogatko SA, Haynes PD, Sathian J, Wade J, Kim J-S, Tan K-J, Breeze J, Salvadori E, Horsfield AP, Oxborrow Met al., 2016, Molecular design of a room-temperature maser, The Journal of Physical Chemistry C, Vol: 120, Pages: 8251-8260, ISSN: 1932-7447

Journal article

Poli E, Elliott JD, Ratcliff LE, Andrinopoulos L, Dziedzic J, Hine NDM, Mostofi AA, Skylaris C-K, Haynes PD, Teobaldi Get al., 2016, The potential of imogolite nanotubes as (co-)photocatalysts: a linear-scaling density functional theory study, Journal of Physics-Condensed Matter, Vol: 28, ISSN: 1361-648X

We report a linear-scaling density functional theory (DFT) study of the structure, wall-polarization absolute band-alignment and optical absorption of several, recently synthesized, open-ended imogolite (Imo) nanotubes (NTs), namely single-walled (SW) aluminosilicate (AlSi), SW aluminogermanate (AlGe), SW methylated aluminosilicate (AlSi-Me), and double-walled (DW) AlGe NTs. Simulations with three different semi-local and dispersion-corrected DFT-functionals reveal that the NT wall-polarization can be increased by nearly a factor of four going from SW-AlSi-Me to DW-AlGe. Absolute vacuum alignment of the NT electronic bands and comparison with those of rutile and anatase TiO2 suggest that the NTs may exhibit marked propensity to both photo-reduction and hole-scavenging. Characterization of the NTs' band-separation and optical properties reveal the occurrence of (near-)UV inside–outside charge-transfer excitations, which may be effective for electron–hole separation and enhanced photocatalytic activity. Finally, the effects of the NTs' wall-polarization on the absolute alignment of electron and hole acceptor states of interacting water (H2O) molecules are quantified and discussed.

Journal article

Zuehlsdorff TJ, Hine NDM, Payne MC, Haynes PDet al., 2015, Linear-scaling time-dependent density-functional theory beyond the Tamm-Dancoff approximation: obtaining efficiency and accuracy with in situ optimised local orbitals, Journal of Chemical Physics, Vol: 143, Pages: 1-13, ISSN: 0021-9606

We present a solution of the full time-dependent density-functional theory (TDDFT) eigenvalue equation in the linear response formalism exhibiting a linear-scaling computational complexity with system size, without relying on the simplifying Tamm-Dancoff approximation (TDA). The implementation relies on representing the occupied and unoccupied subspaces with two different sets of in situ optimised localised functions, yielding a very compact and efficient representation of the transition density matrix of the excitation with the accuracy associated with a systematic basis set. The TDDFT eigenvalue equation is solved using a preconditioned conjugate gradient algorithm that is very memory-efficient. The algorithm is validated on a small test molecule and a good agreement with results obtained from standard quantum chemistry packages is found, with the preconditioner yielding a significant improvement in convergence rates. The method developed in this work is then used to reproduce experimental results of the absorption spectrum of bacteriochlorophyll in an organic solvent, where it is demonstrated that the TDA fails to reproduce the main features of the low energy spectrum, while the full TDDFT equation yields results in good qualitative agreement with experimental data. Furthermore, the need for explicitly including parts of the solvent into the TDDFT calculations is highlighted, making the treatment of large system sizes necessary that are well within reach of the capabilities of the algorithm introduced here. Finally, the linear-scaling properties of the algorithm are demonstrated by computing the lowest excitation energy of bacteriochlorophyll in solution. The largest systems considered in this work are of the same order of magnitude as a variety of widely studied pigment-protein complexes, opening up the possibility of studying their properties without having to resort to any semiclassical approximations to parts of the protein environment.

Journal article

Corsini NR, Zhang Y, Little WR, Karatutlu A, Ersoy O, Haynes PD, Molteni C, Hine ND, Hernandez I, Gonzalez J, Rodriguez F, Brazhkin VV, Sapelkin Aet al., 2015, Pressure-induced amorphization and a new high density amorphous metallic phase in matrix-free Ge nanoparticles, Nano Letters, Vol: 15, Pages: 7334-7340, ISSN: 1530-6992

Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ∼5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.

Journal article

Abdulla M, Refson K, Friend RH, Haynes PDet al., 2015, A first-principles study of the vibrational properties of crystalline tetracene under pressure., Journal of Physics: Condensed Matter, Vol: 27, Pages: 375402-375402, ISSN: 0953-8984

We present a comprehensive study of the hydrostatic pressure dependence of the vibrational properties of tetracene using periodic density-functional theory (DFT) within the local density approximation (LDA). Despite the lack of van der Waals dispersion forces in LDA we find good agreement with experiment and are able to assess the suitability of this approach for simulating conjugated organic molecular crystals. Starting from the reported x-ray structure at ambient pressure and low temperature, optimized structures at ambient pressure and under 280 MPa hydrostatic pressure were obtained and the vibrational properties calculated by the linear response method. We report the complete phonon dispersion relation for tetracene crystal and the Raman and infrared spectra at the centre of the Brillouin zone. The intermolecular modes with low frequencies exhibit high sensitivity to pressure and we report mode-specific Grüneisen parameters as well as an overall Grüneisen parameter [Formula: see text]. Our results suggest that the experimentally reported improvement of the photocurrent under pressure may be ascribed to an increase in intermolecular interactions as also the dielectric tensor.

Journal article

Haynes PD, 2015, Computing the Optical Properties of Large Systems Supervisor's Foreword, COMPUTING THE OPTICAL PROPERTIES OF LARGE SYSTEMS, Publisher: SPRINGER-VERLAG BERLIN, Pages: V-VI, ISBN: 978-3-319-19769-2

Book chapter

Goode AE, Hine NDM, Chen S, Bergin SD, Motskin M, Gonzalez Carter DA, Dexter DT, Shaffer MSP, Ryan MP, Haynes PD, Porter AE, McComb DWet al., 2014, Electron microscopic characterization of functionalized multi-walled carbon nanotubes and their interactions with the blood brain barrier, Pages: 1744-1745, ISSN: 1431-9276

Conference paper

Goode AE, Hine NDM, Chen S, Bergin SD, Shaffer MSP, Ryan MP, Haynes PD, Porter AE, McComb DWet al., 2014, Mapping functional groups on oxidised multiwalled carbon nanotubes at the nanometre scale, CHEMICAL COMMUNICATIONS, Vol: 50, Pages: 6744-6747, ISSN: 1359-7345

Journal article

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