James C Womack

University of Bristol | UB · Advanced Computing Research Centre

The evaluation of molecular integrals is a vital but computationally expensive part of electronic structure calculations. This computational expense is particularly problematic for the explicitly correlated methods, in which complicated and numerous integrals over more than two-electrons must be evaluated. The successful R12/F12 methods overcome th...

The solution of the Poisson equation is a crucial step in electronic structure calculations, yielding the electrostatic potential—a key component of the quantum mechanical Hamiltonian. In recent decades, theoretical advances and increases in computer performance have made it possible to simulate the electronic structure of extended systems in compl...

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), expres...

Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and...

Density functional theory (DFT) has become an engine for driving ab-initio quantum mechanical simulations spanning a vast range of applications. However, conventional DFT has limitations of the accessible system size due to computational expense. Recent progress on linear scaling DFT methods has enabled us to investigate larger systems. In this pap...

Electron localisation descriptors, such as the electron localisation function (ELF) and localisedorbital locator (LOL) provide a visual tool for interpreting the results of electronic structurecalculations. The descriptors produce a quantumvalence shell electron pair repulsion (VSEPR)representation, indicating the localisation of electron pairs int...

We present the implementation of a hybrid continuum-atomistic model for including the effects of surrounding electrolyte in large-scale density functional theory (DFT) calculations within the ONETEP linear-scaling DFT code, which allows the simulation of large complex systems such as electrochemical interfaces. The model represents the electrolyte...

We present the implementation of a hybrid continuum-atomistic model for including the effects of surrounding electrolyte in large-scale density functional theory (DFT) calculations within the ONETEP linear-scaling DFT code, which allows the simulation of large complex systems such as electrochemical interfaces. The model represents the electrolyte...

We present a method for computing excitation energies for molecules in solvent, based on the combination of a minimal parameter implicit solvent model and the equation-of-motion coupled-cluster singles and doubles method (EOM-CCSD). In this method, the solvent medium is represented by a smoothly varying dielectric function, constructed directly fro...

Implicit solvent models provide a simple, yet accurate means to incorporate solvent effects into electronic structure calculations. Such models avoid the computational expense of explicitly modelling solvent molecules by representing the solvent implicitly, for example as a polarizable dielectric medium. In this report, we describe the implementati...

The VV10 and rVV10 nonlocal correlation functionals are consistently implemented and assessed, with the goal of determining if the rVV10 nonlocal correlation functional can replace the VV10 nonlocal correlation functional in the recently-developed B97M-V density functional, to give the B97M-rV density functional. Along the way, four density functio...

The principal challenge in using explicitly correlated wavefunctions for molecules is the evaluation of nonfactorizable integrals over the coordinates of three or more electrons. Immense progress was made in tackling this problem through the introduction of a single-particle resolution of the identity. Decompositions of sufficient accuracy can be a...