Efficient implementation of a van der Waals density functional: Application to double-wall carbon nanotubes

TL;DR

This paper introduces an efficient computational method for van der Waals density functionals, significantly reducing calculation time and enabling accurate modeling of interactions in large systems like double-wall carbon nanotubes.

Contribution

The authors develop a fast Fourier transform-based implementation of the van der Waals density functional, improving computational efficiency for large-scale systems.

Findings

Achieved N log(N) computational scaling.

Accurately calculated binding energies of carbon nanotubes.

Determined energy barriers for nanotube translation and rotation.

Abstract

We present an efficient implementation of the van der Waals density functional of Dion et al [Phys. Rev. Lett. 92, 246401 (2004)], which expresses the nonlocal correlation energy as a double spacial integral. We factorize the integration kernel and use fast Fourier transforms to evaluate the selfconsistent potential, total energy, and atomic forces, in N log(N) operations. The resulting overhead in total computational cost, over semilocal functionals, is very moderate for medium and large systems. We apply the method to calculate the binding energies and the barriers for relative translation and rotation in double-wall carbon nanotubes.