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New 'low-cost' electronic structure methods for large systems

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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 radon2. The PTB method aims primarily at reproducing the one-particle density matrix of a DFT reference calculation with the accurate wB97X-V3 range-separated hybrid (RSH) density functional in exactly the same AO basis. The combination of wB97X(-V) with vDZP/ECP and an adjusted D4 dispersion correction defines a new member in our hierarchy of efficient composite electronic structure methods, termed wB97X-3c2. The basis set optimization concept is furthermore applied to a minimal set of AOs which – as a totally new ingredient – is made adaptive, i.e., radially different for symmetry distinct atoms in a molecule. This q-vSZP set4 forms the basis of our third-generation tight-binding model GP3 -xTB which includes non-local Fock-exchange as well as other new many-center Hamiltonian terms (e.g., atomic correction potentials, ACP ). It aims at general purpose (GP) applicability in chemistry and more closely approaches DFT accuracy than previous semi-empirical methods at only slightly increased computational cost. When the number of primitive Gaussians in q-vSZP is somewhat reduced, and this basis is coupled with wB97M-D45 and ACPs, an extremely efficient new 3c-composite method dubbed wB97M-3c is obtained.

  1. S. Grimme, M. Müller, A. Hansen, J. Chem. Phys., 158 (2023), 124111
  2. M. Müller, A. Hansen, S. Grimme, J. Chem. Phys. 158 (2023), 014103
  3. N. Mardirossian and M. Head-Gordon, Phys. Chem. Chem. Phys. 16 (2016), 9904
  4. M. Müller, A. Hansen, S. Grimme, J. Chem. Phys., in press.
  5. N. Mardirossian and M. Head-Gordon, J. Chem. Phys. 144 (2016), 214110

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