Speaker
Description
All widely used semi-empirical quantum chemical methods like PM6, DFTB, or
GFN-xTB are formulated in a (almost) minimal basis set of atomic
orbitals, which limits the achievable accuracy for many important
chemical properties. Recently, we proposed a new special purpose tight-binding (TB) electronic Hamiltonian termed PTB$^{[1]}$ which is expressed in an accurate polarized valence double-zeta AO basis set (vDZP). The basis has been specially optimized
in molecular DFT calculations using standard ECPs for all elements up to
radon$^{[2]}$. The PTB method aims primarily at reproducing the one-particle density matrix
of a DFT reference calculation with the $\omega$B97X-V range-separated hybrid density
functional$^{[3]}$ in exactly the same AO basis. The combination of $\omega$B97X(-V) with vDZP/ECP
and an adjusted D4 dispersion correction defines a new member in our hierarchy of efficient
composite electronic structure methods, termed $\omega$B97X-3c$^{[2]}$ and is used as reference.
The PTB procedure is non-self-consistent employing only two matrix diagonalizations, includes new non-local potentials, as well as established parts from GFN-xTB and requires only simple overlap integrals as input. Compared to $\omega$B97X-3c
calculations, speedups of 3-4 orders of magnitude are achieved so that runs for molecules with 100-200 atoms are completed in a few seconds of computation time on standard desktop computers. The use of the PTB density in typical computational chemistry applications as well as for non-SCF-iterative DFT-GGA schemes is discussed.
[1] S. Grimme, M. Mueller, A. Hansen, J. Chem. Phys., 158 (2023) 124111
[2] M. Mueller, A. Hansen, S. Grimme, J. Chem. Phys. 158 (2023) 014103
[3] N. Mardirossian and M. Head-Gordon, Phys. Chem. Chem. Phys. 16 (2016) 9904
