Tutorial: Absorption spectra and excitations from real time TD-DFTB

FRANCO BONAFÉ; CRISTIÁN G SÁNCHEZ

Beijing

Workshop; International CECAM-Workshop & Tutorial on Approximate Quantum Methods in the ab initio World; 2016

Centre Européen de Calcul Atomique et Moléculaire

This tutorial is aimed at presenting to the community a new implementation of a computational method to calculate absorption spectra of molecules and nanostructures. The method implemented in the DFTB+ package (http://dftb-plus.info/) is based on the real-time, numerical propagation of the density matrix of a system after a delta-like perturbation with an external electric field, followed by a deconvolution of the dipole moment. This yields the polarizability in the frequency domain, which is proportional to the absorption cross section. The main advantage of this method is the possibility to study large systems given a sufficiently large computational system is used to run the simulations, since the scaling of the time-consuming part is of O(N^3), instead of the O(N^6) scaling of the alternative method (linear response TDDFTB).