Absorption Properties of Large Complex Molecular Systems: The DFTB/Fluctuating Charge Approach.

Piero Lafiosca,Chiara Cappelli,Tommaso Giovannini,Sara Gómez

doi:10.1021/acs.jctc.1c01066

Piero Lafiosca, Chiara Cappelli + Show 2 more

Open Access

https://doi.org/10.1021/acs.jctc.1c01066

Copy DOI

Abstract

We report on the first formulation of a novel polarizable QM/MM approach, where the density functional tight binding (DFTB) is coupled to the fluctuating charge (FQ) force field. The resulting method (DFTB/FQ) is then extended to the linear response within the TD-DFTB framework and challenged to study absorption spectra of large condensed-phase systems.

Highlights

The theoretical modeling of large molecular systems, with application in biological and technological fields, is one of the most challenging tasks for theoretical and computational chemistry.[1,2] the description of large molecular systems requires the treatment of a large number of degrees of freedom, from both nuclear and electronic points of view.[1,2] For this reason, high-level quantum mechanics (QM) methods are usually not applicable because they are usually associated with an unfavorable scaling with the number of atoms.[3]
The self-consistent charge density functional tight binding (DFTB) approach (SCC-DFTB), which corresponds to a second-order expression of the KS energy, has been successfully applied to the calculation of energies, geometries, and vibrational frequencies of small organic molecules; its accuracy when compared with experimental values is comparable to that of full density functional theory (DFT) calculations performed with a double-ζ plus polarization basis set.[17]
We have substantially extended the applicability of the polarizable QM/FQ approach by proposing a novel polarizable QM/FQ scheme based on the DFTB approach for the QM portion, allowing for the treatment of large, complex biomolecular systems

Summary

INTRODUCTION

The theoretical modeling of large molecular systems, with application in biological and technological fields, is one of the most challenging tasks for theoretical and computational chemistry.[1,2] the description of large molecular systems requires the treatment of a large number of degrees of freedom, from both nuclear and electronic points of view.[1,2] For this reason, high-level quantum mechanics (QM) methods are usually not applicable because they are usually associated with an unfavorable scaling with the number of atoms (and electrons).[3]. One of the most used is the density functional tight binding (DFTB) approach.[15−17] The theoretical starting point of such method is the density functional theory (DFT) energy in the Kohn−Sham (KS) framework, expressed by means of a linear combination of atomic orbitals (LCAO) over a minimal basis set This quantity is approximated by means of a Taylor expansion with respect to a reference density truncated at different orders by generating a hierarchy of DFTB methods.[15] In particular, the self-consistent charge DFTB approach (SCC-DFTB), which corresponds to a second-order expression of the KS energy, has been successfully applied to the calculation of energies, geometries, and vibrational frequencies of small organic molecules; its accuracy when compared with experimental values is comparable to that of full DFT calculations performed with a double-ζ plus polarization basis set.[17] a timedependent DFTB (TD-DFTB) approach has been developed to calculate excitation energies in a tight-binding fashion.[18,19] it has been shown that the standard pure or hybrid DFT functionals are not able to accurately treat charge-transfer excitations because their extension to the corresponding longrange-corrected versions is necessary.[20,21] In this context, the time-dependent long-range-corrected DFTB approach (TDLC-DFTB)[22] has recently been proposed and explicitly designed for the treatment of charge-transfer states in large chromophores.

THEORY

COMPUTATIONAL DETAILS

NUMERICAL RESULTS

■ ACKNOWLEDGMENTS

■ REFERENCES