Neil Drummond's Home Page

Neil Drummond

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… to my website. My email address is "n.drummond", followed by "@", followed by "lancaster.ac.uk".

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My Research: First-Principles Calculations of Material Properties

Electronic-structure calculation and quantum Monte Carlo simulation

Most properties of solids and molecules are determined by the behaviour of the electrons that bind their atoms together. The ability to make quantitative predictions about this behaviour is therefore of great importance in a wide range of sciences, from solid-state physics to biochemistry. However, calculating the distribution and energies of electrons in materials—the electronic structure—is a nontrivial problem because of the need to simulate large numbers of strongly interacting particles.

Quantum Monte Carlo (QMC) methods enable the calculation of the electronic structures of solids and molecules with unrivalled accuracy. The methods are stochastic, generating random sets of electron coordinates with the appropriate distribution. Useful quantities, such as energies, are recovered from these data using statistical methods. All my QMC calculations are carried out using the CASINO code, of which I am one of the authors.

Here are some of the projects I am working on / have worked on:

Binding and optoelectronic properties of two-dimensional materials

Two-dimensional (2D) materials such as graphene, silicene, hexagonal boron nitride and transition-metal dichalcogenides (MoS2, MoSe2, MoTe2, NbSe2, TaS2, WS2, WSe2, WTe2, …) are currently of enormous interest in physics, chemistry and materials science. 2D materials are potentially of great technological importance due to their extreme and unusual electronic, optical and mechanical properties. In collaboration with Marcin Szyniszewski, Ryan Hunt, David Thomas, Yassmin Asiri, Elaheh Mostaani, Viktor Zólyomi and Vladimir Fal'ko, I am using QMC and density functional theory methods to calculate and explore many different aspects of these materials. In particular I am investigating the nature and strength of the van der Waals attraction between 2D materials, to understand how they interact with each other, and how they stack to form layered heterostructures. I am also studying excitons, trions and biexcitons (complexes of charge carriers, resembling 2D hydrogen atoms, H− ions and H2 molecules), which play a key role in the optical properties of semiconducting transition-metal dichalcogenides. Lastly I am interested in the mechanical properties and electronic structure of novel 2D materials such as indium and gallium chalcogenides (InS, InSe, InTe, GaS, GaSe and GaTe).

Molecular hydrogen at high pressure

Hydrogen makes up about three quarters of the observed mass in the universe. Hydrogen has been studied extensively, yet there are many unanswered basic questions about its phase diagram. Establishing the atomic structure of high-pressure phases of hydrogen is challenging because hydrogen only scatters X-rays weakly, and the energy differences between competing structures are tiny. In collaboration with Jonathan Lloyd-Williams, Bartomeu Monserrat, Pablo López Ríos, Chris Pickard and Richard Needs of Cambridge University I am using QMC methods to determine the atomic structures of Phases II, III and IV of solid hydrogen at pressures of up to 400 GPa. This work involves use of Oak Ridge Leadership Computing Facility's computer Titan.

Behaviour of positrons immersed in electron gases

I have used both density functional theory (DFT) and QMC methods to calculate the behaviour of positrons immersed in electron gases. In particular, I have calculated the immersion energy, annihilation rate and momentum density of the annihilation radiation as a function of the density of the electron gas. These data will facilitate the interpretation of the results of positron annihilation experiments, in which positrons are injected into metals or semiconductors in order to learn about the type and concentration of defects that are present in the sample.

van der Waals interactions between thin metallic wires and layers

I have used QMC to calculate the van der Waals interaction between pairs of thin, metallic wires and layers, modelled by 1D and 2D homogeneous electron gases. Surprisingly, the form of interaction between 1D conductors assumed in many current models of carbon nanotubes (for example, those that use Lennard-Jones potentials between pairs of atoms) can be shown to be qualitatively wrong.

Optical and chemical properties of hydrogen-terminated carbon nanoparticles

C29H36 HOMO C29H36 LUMO
Highest occupied (left) and lowest unoccupied (right) molecular orbitals of the diamondoid C29H36.

Hydrogen-terminated carbon nanoparticles—diamondoids—are expected to have several technologically useful optoelectronic properties. The optical gap of diamond is in the ultraviolet range, and quantum confinement effects are expected to raise diamondoid optical gaps to even higher energies, enabling a unique set of sensing applications. Furthermore, it has been demonstrated that some hydrogen-terminated diamond surfaces exhibit negative electron affinities, suggesting that diamondoids could also have this property. This would open up the possibility of coating surfaces with diamondoids to produce new low-voltage electron-emission devices.

Measuring the optical gaps of diamondoids has proved to be challenging, due to the difficulty in isolating and characterising particular molecules. I have carried out QMC calculations designed to resolve experimental and theoretical controversies over the optoelectronic properties of diamondoids. My QMC results show that quantum confinement effects disappear in diamondoids larger than one nanometre in diameter, which actually turn out to have gaps below that of bulk diamond. This differs from the behaviour found in silicon or germanium nanoparticles, and is caused by the diffuse nature of the lowest unoccupied molecular orbital in diamondoids. In addition, the QMC calculations predict a negative electron affinity for diamondoids of up to one nanometre in diameter, again resulting from the delocalised nature of the lowest unoccupied molecular orbital.

Equation of state of solid neon

van der Waals forces are of fundamental importance in a wide range of chemical and biological processes, including many that are now being investigated using first-principles electronic-structure methods. I have compared the accuracy with which different electronic-structure methods describe van der Waals bonding by studying solid neon, which is bound together by van der Waals forces, and is therefore an ideal test system for carrying out such a comparison.

I have used the DFT and QMC methods to calculate the zero-temperature equation of state (the relationship between pressure and density) for solid neon. The DFT equation of state depends strongly on the choice of exchange–correlation functional, whereas the QMC equation of state is very close to the experimental results. This implies that, unlike DFT, QMC is able to give an accurate treatment of van der Waals bonding in real materials.

Wigner crystallisation of the homogeneous electron gas

I have used QMC to study the low density behaviour of the homogeneous electron gas. This system consists of a set of electrons moving in a uniform, neutralising, positively charged background. It serves as a model for the behaviour of the free electrons in a metal or semiconductor, and is also of fundamental interest as the simplest fully interacting quantum many-body system. The electron gas exists in a fluid phase at high density, but crystallises at low density, as was first pointed out by Wigner in the 1930s. I have calculated the density at which the homogeneous electron gas crystallises.

Reciprocal lattice points in a finite 2D homogeneous electron gas
Shells of plane-wave orbitals in a 2D homogeneous electron gas. Filled circles indicate orbitals that are occupied in the ground state; unfilled circles indicate orbitals that are unoccupied in the ground state.		I have also used QMC methods to calculate the quasiparticle effective mass of the 2D homogeneous electron gas, which is a model for the charge carriers in a layered semiconductor. The effective mass is the most important parameter in a phenomenological theory of the properties of interacting electron gases called Fermi liquid theory, but its behaviour at low density was poorly understood.

Theoretical and technical developments to the QMC algorithms

  • I have worked on the development of methods for obtaining the energy per particle in an infinite crystal from QMC calculations of the energy per particle in a small simulation cell subject to periodic boundary conditions.
  • I have worked on the development of new forms of trial many-electron wave function. PhD student Clio Johnson and I are currently developing new types of backflow correlation.
  • I have developed a rapid and reliable method for optimising the most important class of parameters in QMC trial wave functions by minimising the unreweighted variance of the local energy.
  • I am one of the authors of the QMC code CASINO.

Studies of minerals in the Earth's lower mantle

In the absence of experimental data, computer simulation can be used to establish the properties of materials. I have studied the mineral magnesium oxide, which is found in the Earth's lower mantle, using density-functional theory. I used the quasiharmonic method to determine the equation of state (the relationship between pressure, density and temperature) of magnesium oxide. I have also calculated phonon dispersion curves (relationships between the frequencies of lattice vibrations, their wavelengths and direction). These data are of interest to geophysicists trying to understand the structure and composition of the Earth's interior. This project was carried out at Edinburgh University in collaboration with Graeme Ackland. Further work using my data has been carried out by Damian Swift (Lawrence Livermore National Laboratory). MgO dispersion curve
Phonon dispersion curve of MgO. Solid lines: theoretical results; black dots: results of neutron-scattering experiments.

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Teaching

I teach the following undergraduate modules at Lancaster University:
  • Phys272/273: Mechanics and Variations
  • Phys281: Scientific Programming and Modelling Project
  • Phys481: Advanced Magnetism
I give the following postgraduate lectures in the Department of Physics at Lancaster University:
  • Scientific Computing
I used to teach the following undergraduate modules at Lancaster University:
  • Phys131: Vectors and Vector Algebra - IT Skills (WolframAlpha and Report Writing)
  • Phys135: Optics and Optical Instruments
  • Phys223: Quantum Mechanics
  • Phys375/378: Theoretical Physics Independent Study (Analytical Recipes in Quantum Mechanics)
  • Phys482: Quantum Transport in Low-Dimensional Nanostructures
I used to teach the following graduate course at the Graphene NOWNANO centre for doctoral training (Universities of Lancaster and Manchester):
  • Two-Dimensional Materials From a Solid State Physics Perspective
At Cambridge University I gave a course of graduate lectures in solid state physics at the Cavendish Laboratory and I used to be a supervisor for the NST1A Maths for Natural Sciences course.

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Useful Links

University links

Links to journals and other sources of information

Computer-related links

Miscellaneous links

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List of Publications

  1. M. Szyniszewski, E. Mostaani, A. Knothe, V. Enaldiev, A. C. Ferrari, V. I. Fal'ko and N. D. Drummond, Adhesion and reconstruction of graphene/hexagonal boron nitride heterostructures: a quantum Monte Carlo study, submitted to ACS Nano (2024).
  2. S. Azadi, N. D. Drummond and S. M. Vinko, Quantum Monte Carlo study of the phase diagram of the two-dimensional uniform electron liquid, accepted for publication in Phys. Rev. B (2024). [Preprint: arXiv:2405.00425]
  3. K. Morawetz, V. Ashokan, K. N. Pathak, N. Drummond and G. Cuniberti, Electronic quantum wires in extended quasiparticle picture, Phys. Rev. B 109, 205116 (2024). [Download]
  4. G. J. Bean, N. D. Drummond and J. Ruostekoski, Propagation of light in cold emitter ensembles with quantum position correlations due to static long-range dipolar interactions, Phys. Rev. Research 6, 013078 (2024). [Download]
  5. S. Azadi, N. D. Drummond and S. M. Vinko, Correlation energy of the spin-polarized electron liquid studied using quantum Monte Carlo simulations, Phys. Rev. B 108, 115134 (2023). [Download]
  6. E. Mostaani, R. J. Hunt, D. M. Thomas, M. Szyniszewski, A. R. P. Montblanch, M. Barbone, M. Atatüre, N. D. Drummond and A. C. Ferrari, Charge-carrier complexes in monolayer semiconductors, Phys. Rev. B 108, 035420 (2023). [Download]
  7. K. A. Simula, J. Härkönen, I. Zhelezova, N. D. Drummond, F. Tuomisto and I. Makkonen, Quantum Monte Carlo study of Doppler broadening of positron annihilation radiation in semiconductors and insulators, Phys. Rev. B 108, 045201 (2023). [Download]
  8. I. Amelio, N. D. Drummond, E. Demler, R. Schmidt and A. Imamoglu, Polaron spectroscopy of a bilayer excitonic insulator, Phys. Rev. B 107, 155303 (2023). [Download]
  9. A. Girdhar, V. Ashokan, R. O. Sharma, N. D. Drummond and K. N. Pathak, Wire-width and electron-density dependence of the crossover in the peak of the static structure factor from 2kF→4kF in one-dimensional paramagnetic electron gases, Phys. Rev. B 107, 115414 (2023). [Download]
  10. S. Azadi, N. D. Drummond and S. M. Vinko, Correlation energy of the paramagnetic electron gas at the thermodynamic limit, Phys. Rev. B 107, L121105 (2023). [Download]
  11. G. Cassella, H. Sutterud, S. Azadi, N. D. Drummond, D. Pfau, J. S. Spencer and W. M. C. Foulkes, Discovering quantum phase transitions with fermionic neural networks, Phys. Rev. Lett. 130, 036401 (2023). [Download]
  12. F. Marsusi, E. Mostaani and N. D. Drummond, Quantum Monte Carlo study of three-dimensional Coulomb complexes: trions and biexcitons; hydrogen molecules and ions; helium hydride cations; and positronic and muonic complexes, Phys. Rev. A 106, 062822 (2022). [Download]
  13. K. A. Simula, J. E. Muff, I. Makkonen and N. D. Drummond, Quantum Monte Carlo study of positron lifetimes in solids, Phys. Rev. Lett. 129, 166403 (2022). [Download]
  14. S. Azadi and N. D. Drummond, Low-density phase diagram of the three-dimensional electron gas, Phys. Rev. B 105, 245135 (2022). [Download]
  15. D. M. Thomas, Y. Asiri and N. D. Drummond, Point defect formation energies in graphene from diffusion quantum Monte Carlo and density functional theory, Phys. Rev. B 105, 184114 (2022). [Download]
  16. A. Girdhar, V. Ashokan, N. D. Drummond, K. Morawetz and K. N. Pathak, Electron correlation and confinement effects in quasi-one-dimensional quantum wires at high density, Phys. Rev. B 105, 115140 (2022). [Download]
  17. S. Azadi, N. D. Drummond and W. M. C. Foulkes, Quasiparticle effective mass of the three-dimensional Fermi liquid by quantum Monte Carlo, Phys. Rev. Lett. 127, 086401 (2021). [Download]
  18. R. O. Sharma, N. D. Drummond, V. Ashokan, K. N. Pathak and K. Morawetz, Ground-state properties of electron-electron biwire systems, Phys. Rev. B 104, 035149 (2021). [Download]
  19. S. Slizovskiy, A. Garcia-Ruiz, A. I. Berdyugin, X. Na, T. Taniguchi, K. Watanabe, A. Geim, N. D. Drummond and V. I. Fal'ko, Out-of-plane dielectric susceptibility of graphene in twistronic and Bernal bilayers, Nano Lett. 21, 6678 (2021). [Download]
  20. S. J. Magorrian, V. Zólyomi and N. D. Drummond, Structures of bulk hexagonal post transition metal chalcogenides from dispersion-corrected density functional theory, Phys. Rev. B 103, 094118 (2021). [Download]
  21. R. J. Hunt, B. Monserrat, V. Zólyomi and N. D. Drummond, Diffusion quantum Monte Carlo and GW study of the electronic properties of monolayer and bulk hexagonal boron nitride, Phys. Rev. B 101, 205115 (2020). [Download]
  22. R. J. Needs, M. D. Towler, N. D. Drummond, P. López Ríos and J. R. Trail, Variational and diffusion quantum Monte Carlo calculations with the CASINO code, J. Chem. Phys. 152, 154106 (2020). [Download]
  23. F. Vialla, M. Danovich, D. A. Ruiz-Tijerina, M. Massicotte, P. Schmidt, T. Taniguchi, K. Watanabe, R. J. Hunt, M. Szyniszewski, N. D. Drummond, T. G. Pedersen, V. I. Fal'ko and F. H. L. Koppens, Tuning of impurity-bound interlayer complexes in a van der Waals heterobilayer, 2D Mater. 6, 035032 (2019). [Download]
  24. J. Li, N. D. Drummond, P. Schuck and V. Olevano, Comparing many-body approaches against the real helium atom exact solution, SciPost Phys. 6, 040 (2019). [Download]
  25. D. M. Thomas, R. J. Hunt, N. D. Drummond and M. Hayne, Binding energies of excitonic complexes in type-II quantum rings from diffusion quantum Monte Carlo calculations, Phys. Rev. B 99, 115306 (2019). [Download]
  26. F. Marsusi, N. D. Drummond and M. J. Verstraete, The physics of single-side fluorination of graphene: DFT and DFT+U studies, Carbon 144, 615 (2019). [Download]
  27. V. Ashokan, N. D. Drummond and K. N. Pathak, One-dimensional electron fluid at high density, Phys. Rev. B 98, 125139 (2018). [Download]
  28. R. J. Hunt, M. Szyniszewski, G. I. Prayogo, R. Maezono and N. D. Drummond, Quantum Monte Carlo calculations of energy gaps from first principles, Phys. Rev. B 98, 075122 (2018). [Download]
  29. B. Monserrat, N. D. Drummond, P. Dalladay-Simpson, R. T. Howie, P. López Ríos, E. Gregoryanz, C. J. Pickard and R. J. Needs, Structure and metallicity of phase V of hydrogen, Phys. Rev. Lett. 120, 255701 (2018). [Download]
  30. M. Danovich, D. A. Ruiz-Tijerina, R. J. Hunt, M. Szyniszewski, N. D. Drummond and V. I. Fal'ko, Localized interlayer complexes in heterobilayer transition metal dichalcogenides, Phys. Rev. B 97, 195452 (2018). [Download]
  31. O. Witham, R. J. Hunt and N. D. Drummond, Stability of trions in coupled quantum wells modeled by two-dimensional bilayers, Phys. Rev. B 97, 075424 (2018). [Download]
  32. E. Mostaani, M. Szyniszewski, C. H. Price, R. Maezono, M. Danovich, R. J. Hunt, N. D. Drummond and V. I. Fal'ko, Diffusion quantum Monte Carlo study of excitonic complexes in two-dimensional transition-metal dichalcogenides, Phys. Rev. B 96, 075431 (2017). [Download]
  33. M. Szyniszewski, E. Mostaani, N. D. Drummond and V. I. Fal'ko, Binding energies of trions and biexcitons in two-dimensional semiconductors from diffusion quantum Monte Carlo calculations, Phys. Rev. B 95, 081301(R) (2017). [Download]
  34. S. Azadi, N. D. Drummond and W. M. C. Foulkes, Nature of the metallization transition in solid hydrogen, Phys. Rev. B 95, 035142 (2017). [Download]
  35. N. D. Drummond, J. R. Trail and R. J. Needs, Trail-Needs pseudopotentials in quantum Monte Carlo calculations with plane-wave/blip basis sets, Phys. Rev. B 94, 165170 (2016). [Download]
  36. M. Danovich, I. L. Aleiner, N. D. Drummond and V. I. Fal'ko, Fast relaxation of photo-excited carriers in 2-D transition metal dichalcogenides, IEEE J. Sel. Top. Quantum Electron. 23, 6000105 (2016). [Download]
  37. G. G. Spink, P. López Ríos, N. D. Drummond and R. J. Needs, Trion formation in a two-dimensional hole-doped electron gas, Phys. Rev. B 94, 041410(R) (2016). [Download]
  38. E. Mostaani, B. Monserrat, N. D. Drummond and C. J. Lambert, Quasiparticle and excitonic gaps of one-dimensional carbon chains, Phys. Chem. Chem. Phys. 18, 14810 (2016). [Download]
  39. F. Liu, S. Zheng, A. Chaturvedi, V. Zólyomi, J. Zhou, Q. Fu, C. Zhu, P. Yu, Q. Zeng, N. D. Drummond, H. J. Fan, C. Kloc, V. I. Fal'ko, X. He and Z. Liu, Optoelectronic properties of atomically thin ReSSe with weak interlayer coupling, Nanoscale 8, 5826 (2016). [Download]
  40. E. Mostaani, N. D. Drummond and V. I. Fal'ko, Quantum Monte Carlo calculation of the binding energy of bilayer graphene, Phys. Rev. Lett. 115, 115501 (2015). [Download]
  41. N. D. Drummond, B. Monserrat, J. H. Lloyd-Williams, P. López Ríos, C. J. Pickard and R. J. Needs, Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures, Nat. Commun. 6, 7794 (2015). [Download]
  42. A. Kormányos, G. Burkard, M. Gmitra, J. Fabian, V. Zólyomi, N. D. Drummond and V. I. Fal'ko, k.p theory for two-dimensional transition metal dichalcogenide semiconductors, 2D Mater. 2, 022001 (2015). [Download]
  43. B. Ganchev, N. D. Drummond, I. Aleiner and V. Fal'ko, Three-particle complexes in two-dimensional semiconductors, Phys. Rev. Lett. 114, 107401 (2015). [Download]
  44. W. W. Tipton, N. D. Drummond and R. G. Hennig, Importance of high-angular-momentum channels in pseudopotentials for quantum Monte Carlo, Phys. Rev. B 90, 125110 (2014). [Download]
  45. V. Zólyomi, N. D. Drummond and V. I. Fal'ko, Electrons and phonons in single layers of hexagonal indium chalcogenides from ab initio calculations, Phys. Rev. B 89, 205416 (2014). [Download]
  46. A. Kormányos, V. Zólyomi, N. D. Drummond and G. Burkard, Spin–orbit coupling, quantum dots and qubits in transition metal dichalcogenides, Phys. Rev. X 4, 011034 (2014). [Download]
  47. F. Liu, H. Shimotani, H. Shang, T. Kanagasekaran, V. Zólyomi, N. D. Drummond, V. I. Fal'ko and K. Tanigaki, High-sensitivity photodetectors based on multilayer GaTe flakes, ACS Nano 8, 752 (2014). [Download]
  48. B. Monserrat, N. D. Drummond, C. J. Pickard and R. J. Needs, Electron–phonon coupling and the metalization of solid helium at terapascal pressures, Phys. Rev. Lett. 112, 055504 (2014). [Download]
  49. A. J. Misquitta, R. Maezono, N. D. Drummond, A. J. Stone and R. J. Needs, Anomalous nonadditive dispersion interactions in systems of three one-dimensional wires, Phys. Rev. B 89, 045140 (2014). [Download]
  50. G. G. Spink, R. J. Needs, and N. D. Drummond, Quantum Monte Carlo study of the three-dimensional spin-polarized homogeneous electron gas, Phys. Rev. B 88, 085121 (2013). [Download]
  51. N. D. Drummond and R. J. Needs, Quantum Monte Carlo calculation of the Fermi liquid parameters of the two-dimensional homogeneous electron gas, Phys. Rev. B 88, 035133 (2013). [Download]
  52. A. Kormányos, V. Zólyomi, N. D. Drummond, P. Rakyta, G. Burkard and V. I. Fal'ko, Monolayer MoS2: trigonal warping, "Γ-valley" and spin–orbit coupling effects, Phys. Rev. B 88, 045416 (2013). [Download]
  53. V. Zólyomi, N. D. Drummond and V. I. Fal'ko, Band structure and optical transitions in atomic layers of hexagonal gallium chalcogenides, Phys. Rev. B 87, 195403 (2013). [Download]
  54. B. Monserrat, N. D. Drummond and R. J. Needs, Anharmonic vibrational properties in periodic systems: energy, electron–phonon coupling, and stress, Phys. Rev. B 87, 144302 (2013). [Download]
  55. N. D. Drummond and R. J. Needs, Diffusion quantum Monte Carlo calculation of the quasiparticle effective mass of the two-dimensional homogeneous electron gas, Phys. Rev. B 87, 045131 (2013). [Download]
  56. P. López Ríos, P. Seth, N. D. Drummond and R. J. Needs, Framework for constructing generic Jastrow correlation factors, Phys. Rev. E 86, 036703 (2012). [Download]
  57. N. D. Drummond, V. Zólyomi and V. I. Fal'ko, Electrically tunable band gap in silicene, Phys. Rev. B 85, 075423 (2012). [Download]
  58. F. Marsusi, J. Sabbaghzadeh and N. D. Drummond, Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts, Phys. Rev. B 84, 245315 (2011). [Download]
  59. N. D. Drummond, P. López Ríos, C. J. Pickard and R. J. Needs, Quantum Monte Carlo study of a positron in an electron gas, Phys. Rev. Lett. 107, 207402 (2011). [Download]
  60. R. M. Lee, G. J. Conduit, N. Nemec, P. López Ríos and N. D. Drummond, Strategies for improving the efficiency of quantum Monte Carlo calculations, Phys. Rev. E 83, 066706 (2011). [Download]
  61. R. M. Lee and N. D. Drummond, Ground-state properties of the one-dimensional electron liquid, Phys. Rev. B 83, 245114 (2011). [Download]
  62. N. D. Drummond, N. R. Cooper, R. J. Needs and G. V. Shlyapnikov, Quantum Monte Carlo calculation of the zero-temperature phase diagram of the two-component fermionic hard-core gas in two dimensions, Phys. Rev. B 83, 195429 (2011). [Download]
  63. R. Maezono, N. D. Drummond, A. Ma and R. J. Needs, Diamond to β-tin phase transition in Si within diffusion quantum Monte Carlo, Phys. Rev. B 82, 184108 (2010). [Download]
  64. S. J. Binnie, S. J. Nolan, N. D. Drummond, D. Alfè, N. L. Allan, F. R. Manby and M. J. Gillan, Bulk and surface energetics of crystalline lithium hydride: Benchmarks from quantum Monte Carlo and quantum chemistry, Phys. Rev. B 82, 165431 (2010). [Download]
  65. Y. Kita, M. Tachikawa, N. D. Drummond and R. J. Needs, A variational Monte Carlo study of positronic compounds using inhomogeneous backflow transformations, Chem. Lett. 39, 1136 (2010). [Download]
  66. N. D. Drummond, P. López Ríos, C. J. Pickard and R. J. Needs, First-principles method for impurities in quantum fluids: Positron in an electron gas, Phys. Rev. B 82, 035107 (2010). [Download]
  67. R. J. Needs, M. D. Towler, N. D. Drummond and P. López Ríos, Continuum variational and diffusion quantum Monte Carlo calculations, J. Phys.: Condens. Matter 22, 023201 (2010). [Download]
  68. N. D. Drummond and R. J. Needs, Quantum Monte Carlo calculation of the energy band and quasiparticle effective mass of the two-dimensional Fermi fluid, Phys. Rev. B 80, 245104 (2009). [Download]
  69. C.-R. Hsing, C.-M. Wei, N. D. Drummond and R. J. Needs, Quantum Monte Carlo studies of covalent and metallic clusters: accuracy of density functional approximations, Phys. Rev. B 79, 245401 (2009). [Download]
  70. N. D. Drummond and R. J. Needs, Phase diagram of the low-density two-dimensional homogeneous electron gas, Phys. Rev. Lett. 102, 126402 (2009). [Download]
  71. R. M. Lee, N. D. Drummond and R. J. Needs, Exciton–exciton interaction and biexciton formation in bilayer systems, Phys. Rev. B 79, 125308 (2009). [Download]
  72. N. D. Drummond and R. J. Needs, Quantum Monte Carlo study of the ground state of the two-dimensional Fermi fluid, Phys. Rev. B 79, 085414 (2009). [Download]
  73. N. D. Drummond, R. J. Needs, A. Sorouri and W. M. C. Foulkes, Finite-size errors in continuum quantum Monte Carlo calculations, Phys. Rev. B 78, 125106 (2008). [Download]
  74. N. D. Drummond and R. J. Needs, van der Waals interactions between thin metallic wires and layers, Phys. Rev. Lett. 99, 166401 (2007). [Download]
  75. N. D. Drummond, Nanomaterials: Diamondoids display their potential, Nat. Nanotechnol. 2, 462 (2007). [Download]
  76. P. López Ríos, A. Ma, N. D. Drummond, M. D. Towler and R. J. Needs, Inhomogeneous backflow transformations in quantum Monte Carlo, Phys. Rev. E 74, 066701 (2006). [Download]
  77. N. D. Drummond, P. López Ríos, A. Ma, J. R. Trail, G. G. Spink, M. D. Towler and R. J. Needs, Quantum Monte Carlo study of the Ne atom and the Ne+ ion, J. Chem. Phys. 124, 224104 (2006). [Download]
  78. N. D. Drummond and R. J. Needs, Quantum Monte Carlo, density functional theory, and pair potential studies of solid neon, Phys. Rev. B 73, 024107 (2006). [Download]
  79. I. G. Gurtubay, N. D. Drummond, M. D. Towler and R. J. Needs, Quantum Monte Carlo calculations of the dissociation energies of three-electron hemibonded radical cationic dimers, J. Chem. Phys. 124, 024318 (2006). [Download]
  80. N. D. Drummond, A. J. Williamson, R. J. Needs and G. Galli, Electron emission from diamondoids: a diffusion quantum Monte Carlo study, Phys. Rev. Lett. 95, 096801 (2005). [Download]
  81. N. D. Drummond and R. J. Needs, Variance-minimization scheme for optimizing Jastrow factors, Phys. Rev. B 72, 085124 (2005). [Download]
  82. A. Ma, M. D. Towler, N. D. Drummond and R. J. Needs, Scheme for adding electron–nucleus cusps to Gaussian orbitals, J. Chem. Phys. 122, 224322 (2005). [Download]
  83. A. Ma, M. D. Towler, N. D. Drummond and R. J. Needs, All-electron quantum Monte Carlo calculations for the noble gas atoms He to Xe, Phys. Rev. E 71, 066704 (2005). [Download]
  84. M. Y. J. Tan, N. D. Drummond and R. J. Needs, Exciton and biexciton energies in bilayer systems, Phys. Rev. B 71, 033303 (2005). [Download]
  85. N. D. Drummond, M. D. Towler and R. J. Needs, Jastrow correlation factor for atoms, molecules, and solids, Phys. Rev. B 70, 235119 (2004). [Download]
  86. S.-N. Luo, D. C. Swift, R. N. Mulford, N. D. Drummond and G. J. Ackland, Performance of an ab initio equation of state for MgO, J. Phys.: Condens. Matter 16, 5435 (2004). [Download]
  87. B. Wood, W. M. C. Foulkes, M. D. Towler and N. D. Drummond, Coulomb finite-size effects in quasi-two-dimensional systems, J. Phys.: Condens. Matter 16, 891 (2004). [Download]
  88. N. D. Drummond, Z. Radnai, J. R. Trail, M. D. Towler and R. J. Needs, Diffusion quantum Monte Carlo study of three-dimensional Wigner crystals, Phys. Rev. B 69, 085116 (2004). [Download]
  89. N. D. Drummond and G. J. Ackland, Ab initio quasiharmonic equations of state for dynamically-stabilized soft-mode materials, Phys. Rev. B 65, 184104 (2002). [Download]
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