64 research outputs found
Minimal Basis Iterative Stockholder: Atoms in Molecules for Force-Field Development
Atomic partial charges appear in the Coulomb term of many force-field models
and can be derived from electronic structure calculations with a myriad of
atoms-in-molecules (AIM) methods. More advanced models have also been proposed,
using the distributed nature of the electron cloud and atomic multipoles. In
this work, an electrostatic force field is defined through a concise
approximation of the electron density, for which the Coulomb interaction is
trivially evaluated. This approximate "pro-density" is expanded in a minimal
basis of atom-centered s-type Slater density functions, whose parameters are
optimized by minimizing the Kullback-Leibler divergence of the pro-density from
a reference electron density, e.g. obtained from an electronic structure
calculation. The proposed method, Minimal Basis Iterative Stockholder (MBIS),
is a variant of the Hirshfeld AIM method but it can also be used as a
density-fitting technique. An iterative algorithm to refine the pro-density is
easily implemented with a linear-scaling computational cost, enabling
applications to supramolecular systems. The benefits of the MBIS method are
demonstrated with systematic applications to molecular databases and extended
models of condensed phases. A comparison to 14 other AIM methods shows its
effectiveness when modeling electrostatic interactions. MBIS is also suitable
for rescaling atomic polarizabilities in the Tkatchenko-Sheffler scheme for
dispersion interactions.Comment: 61 pages, 12 figures, 2 table
Stability of charges in titanium compounds and charge transfer to oxygen in titanium dioxide
We investigate the charge density distribution in titanium dioxide, molecular
titanium complexes and a variety of periodic titanium compounds using
delocalization indices and Bader charge analysis. Our results are in agreement
with previous experimental and theoretical investigations on the charge
stability and deviation from formal oxidation states in transition metal
compounds. We present examples for practically relevant redox processes, using
molecular titanium dioxide model systems, that illustrate the failure of formal
oxidation states to account for some redox phenomena. We observe a pronounced
charge stability on titanium for trial systems which are expected to be mainly
ionic. No environment tested by us is capable to reduce the local titanium
charge remainder below one electron.Comment: 9 pages, 2 figures, CCP2017 conference (Paris, France, July 9-13,
2017
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