Wavelet-Based Linear-Response Time-Dependent Density-Functional Theory

TL;DR

This paper implements wavelet-based linear-response TD-DFT in BigDFT, compares it with deMon2k, and demonstrates comparable accuracy and faster convergence, with applications to molecular absorption spectra.

Contribution

It introduces a wavelet-based implementation of linear-response TD-DFT in BigDFT and compares its performance and results with an all-electron Gaussian-type orbital program.

Findings

Comparable excitation energies and spectra between BigDFT and deMon2k.

Faster convergence of density orbitals in BigDFT.

Differences in virtual orbital handling between the two programs.

Abstract

Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BigDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program deMon2k for the calculation of electronic absorption spectra of N2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BigDFT than for deMon2k. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BigDFT, while all virtual orbitals are included in TD-DFT calculations in deMon2k. As a reality check, we report the x-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-amine.