Implementation and benchmark of a long-range corrected functional in the density functional based tight-binding method

Abstract

Bridging the gap between first principles methods and empirical schemes, the density functional based tight-binding method (DFTB) has become a versatile tool in predictive atomistic simulations over the past years. One of the major restrictions of this method is the limitation to local or gradient corrected exchange-correlation functionals. This excludes the important class of hybrid or long-range corrected functionals, which are advantageous in thermochemistry, as well as in the computation of vibrational, photoelectron, and optical spectra. The present work provides a detailed account of the implementation of DFTB for a long-range corrected functional in generalized Kohn-Sham theory. We apply the method to a set of organic molecules and compare ionization potentials and electron affinities with the original DFTB method and higher level theory. The new scheme cures the significant overpolarization in electric fields found for local DFTB, which parallels the functional dependence in first principles density functional theory (DFT). At the same time, the computational savings with respect to full DFT calculations are not compromised as evidenced by numerical benchmark data.

Vibrationally resolved UV/Vis spectroscopy with time-dependent density functional based tight binding

“…However, both these restrictions are likely to be lifted with recent DFTB extensions, i.e. on-site correction 58 and inclusion of exact exchange [60][61][62] , which due to the lack of analytical (excited state) gradients, can not yet be used for the calculation of vibronic fine structure.…”

Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations

“…The semi-empirical density-functional tight-binding (DFTB) method is highly attractive for overcoming size and complexity modeling constraints, but it needs to be carefully assessed to determine the expected accuracy. In this paper, we complement previous efforts [13,14] ( [14] concerns implementing range-separated hybrids in DFTB [15,16]) by assessing DFTB against accurate first-principles GW (Green's function, G, times the screened potential, W) calculations [17][18][19] for the calculation of the IPs and EAs of medium-sized molecules.…”

“…as significant differences in DFTB orbital energies may be expected between the two approaches and as the latter approach is that actually used in the DFTB program and parameters whose results are reported in this paper [14]. Whichever choice is used, the AOs χ µ are typically calculated for a slightly confined atom to emulate the effect of an atom in a molecule.…”

Gaussian polarizable-ion tight binding

“…A smaller Gaussian density smearing can be used in the PPD model as a consequence of the polarizability reduction, which increases the dielectric constant and therefore largely negates the previous changes. This makes clear the need for future research on efficient self-interaction correction methods 48,51,52 for tightbinding in conjunction with the electrostatic multipoles model. We refer to the recently developed long-range corrected DFTB method 48 as a possible solution.…”

“…47 GTB, as an approximate PBE-DFT method, inherits this limitation. 48 We demonstrate this by computing the polarizabilities of a P3HT strand for chain lengths of varying monomer count n, where n = 20 corresponds to a full P3HT chain. The chain segments are terminated with hydrogen.…”