Accurate simulation of electronic absorption and circular dichroism spectra (ECD) in condensed phase is still a challenging task. For large biomolecular or supramolecular systems, quantum mechanical methods based on ab-initio wavefunction theory or first-principles density functional theory (DFT) are not applicable or restricted to the calculation of only a small number of excited states, and more efficient methods have to be used. For this purpose, we have developed simplified variants of time-dependent DFT (sTD-DFT) and Tamm-Dancoff approximated TD-DFT (sTDA-DFT). These approaches are orders of magnitude faster in the excited states calculation than standard TD-DFT. Their efficiency stems from a restricted excitation expansion space and approximated evaluation of two-electron integrals. This enables the routine computation of entire absorption and ECD spectra for large systems. By replacing the preceeding Kohn-Sham DFT calculation with a specifically designed tight-binding procedure, we succeeded in removing the bottleneck in our excited state approach. This ultra-fast scheme, denoted by sTDA-xTB, allows the computation of broad range absorption and ECD spectra for several hundred atoms within a few minutes on a single-core laptop. Spectra can also be computed on snapshots from molecular dynamics (MD) simulations. For the latter, another recently developed tight-binding approach (GFN-xTB) can be used.

Simplified methods for the computation of electronic absorption and circular dichroism spectra

254th National Meeting (2017)

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