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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Improved electronic properties from third-order SCC-DFTB with cost efficient post-SCF extensions.

Steve Kaminski1, Michael Gaus, Marcus Elstner

  • 1Karlsruher Institut für Technologie, Institut für Physikalische Chemie, Karlsruhe, Germany.

The Journal of Physical Chemistry. A
|November 22, 2012
PubMed
Summary
This summary is machine-generated.

Two cost-efficient extensions improve Self-Consistent Field Density Functional Tight Binding (SCC-DFTB) calculations for molecular dipole moments and polarizabilities. These enhancements offer better accuracy at minimal computational cost, though they do not improve infrared and Raman intensity predictions.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Materials Science

Background:

  • Self-Consistent Field Density Functional Tight Binding (SCC-DFTB) is a computationally efficient method for electronic structure calculations.
  • Standard SCC-DFTB methods exhibit inaccuracies in describing molecular charge distribution and electronic polarizability due to approximations in basis sets and partitioning schemes.

Purpose of the Study:

  • To implement and evaluate two cost-efficient post-Self-Consistent Field (SCF) extensions for the SCC-DFTB code.
  • To improve the accuracy of molecular dipole moments and electronic polarizabilities calculated using SCC-DFTB.
  • To assess the impact of these extensions on the prediction of infrared and Raman intensities.

Main Methods:

  • Implementation of the Charge Model 3 (CM3) to correct bond dipole errors and improve molecular charge distribution.
  • Development of a variational approach using scaled dipole integrals to enhance the calculation of electronic molecular polarizability.
  • Empirical parameter fitting against 112 organic molecules using reference data from full density functional calculations with large basis sets.

Main Results:

  • The CM3 extension provides a more accurate description of molecular charge distribution compared to standard Mulliken partitioning.
  • The variational approach for polarizability calculations significantly outperforms standard finite electric field methods, achieving accuracy approximately one order of magnitude better.
  • SCC-DFTB calculations with the implemented extensions yield notably improved molecular dipole moments and polarizabilities with negligible additional computational cost.

Conclusions:

  • The developed post-SCF extensions significantly enhance the accuracy of SCC-DFTB for calculating molecular dipole moments and polarizabilities.
  • These improvements are achieved without a substantial increase in computational expense, making them valuable for large-scale simulations.
  • The current implementations do not lead to improved prediction of relative infrared and Raman intensity patterns compared to ab initio reference data.