# Peter Haynes

Faculty of EngineeringDepartment of Materials

Head of Department of Materials

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### Contact

+44 (0)20 7594 5158p.haynes CV

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### Assistant

Miss Catherine Graham +44 (0)20 7594 3330

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### Location

201BRoyal School of MinesSouth Kensington Campus

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## Publications

Publication Type
Year
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71 results found

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-induceddeformations on the optoelectronic propertiesof nanomaterials is important not only fromthe fundamental point of view, but also for po-tential applications such as stress sensors andelectromechanical devices. Here we describethe novel insights into these piezochromic ef-fects gained from using a linear-scaling den-sity functional theory framework and an elec-tronic enthalpy scheme, which allow us to ac-curately characterize the electronic structure ofCdS nanocrystals with a zincblende-like coreof experimentally relevant size. In particu-lar we focus on unravelling the complex inter-play of size and surface (phenyl) ligands withpressure. We show that pressure-induced de-formations are not simple isotropic scaling ofthe original structures and that the change inHOMO-LUMO gap with pressure results fromtwo competing factors: (i) a bulk-like linear in-crease due to compression, which is offset by(ii) distortions/disorder and, to a lesser ex-tent, orbital hybridization induced by ligandsaffecting the frontier orbitals. Moreover, weobserve that the main peak in the optical ab-sorption spectra is systematically red-shifted orblue-shifted, as pressure is increased up to 5GPa, depending on the presence or absenceof phenyl ligands. These heavily hybridize thefrontier orbitals, causing a reduction in over-lap and oscillator strength, so that at zero pres-sure the lowest energy transition involves deeperhole orbitals than in the case of hydrogen-capped nanocrystals; the application of pressureinduces greater delocalisation over the wholenanocrystals bringing the frontier hole orbitalsinto play and resulting in an unexpected redshift for the phenyl-capped nanocrystals, in partcaused by distortions. In response to a growinginterest in relatively small nanocrystals that canbe difficult to accurately characterize with ex-perimental techniques, this work exemplifies thedetailed understanding of structure-property re-lationships under p

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

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

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

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, ISSN: 0021-9606

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

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

Cole DJ, Chin AW, Hine NDM, Haynes PD, Payne MCet al., 2013, Toward Ab Initio Optical Spectroscopy of the Fenna-Matthews-Olson Complex, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 4, Pages: 4206-4212, ISSN: 1948-7185

Journal article

Silas PK, Haynes PD, Yates JR, 2013, Evolution of the Fermi surface of arsenic through the rhombohedral to simple-cubic phase transition: A Wannier interpolation study, PHYSICAL REVIEW B, Vol: 88, ISSN: 1098-0121

Journal article

Janssen JL, Beaudin J, Hine NDM, Haynes PD, Cote Met al., 2013, Bromophenyl functionalization of carbon nanotubes: an ab initio study, NANOTECHNOLOGY, Vol: 24, ISSN: 0957-4484

Journal article

Corsini NRC, Greco A, Hine NDM, Molteni C, Haynes PDet al., 2013, Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory, JOURNAL OF CHEMICAL PHYSICS, Vol: 139, ISSN: 0021-9606

Journal article

Zuehlsdorff TJ, Hine NDM, Spencer JS, Harrison NM, Riley DJ, Haynes PDet al., 2013, Linear-scaling time-dependent density-functional theory in the linear response formalism, JOURNAL OF CHEMICAL PHYSICS, Vol: 139, ISSN: 0021-9606

Journal article

Lever G, Cole DJ, Hine NDM, Haynes PD, Payne MCet al., 2013, Electrostatic considerations affecting the calculated HOMO-LUMO gap in protein molecules, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 25, ISSN: 0953-8984

Journal article

Ratcliff LE, Haynes PD, 2013, Ab initio calculations of the optical absorption spectra of C-60-conjugated polymer hybrids, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 15, Pages: 13024-13031, ISSN: 1463-9076

Journal article

Avraam PW, Hine NDM, Tangney P, Haynes PDet al., 2012, Fermi-level pinning can determine polarity in semiconductor nanorods, PHYSICAL REVIEW B, Vol: 85, ISSN: 1098-0121

Journal article

Hine NDM, Avraam PW, Tangney P, Haynes PDet al., 2012, Linear-Scaling Density Functional Theory Simulations of Polar Semiconductor Nanorods, 3rd Workshop on Theory, Modelling and Computational Methods for Semiconductor Materials and Nanostructures (TMCS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588

Conference paper

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