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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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Determining quasidiabatic coupled electronic state Hamiltonians using derivative couplings: A normal equations based

Brian N Papas1, Michael S Schuurman, David R Yarkony

  • 1Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.

The Journal of Chemical Physics
|December 3, 2008
PubMed
Summary

This study presents a new method to create accurate quasidiabatic Hamiltonians for multiple electronic states. The approach refines the Hamiltonian

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Area of Science:

  • Quantum Chemistry
  • Theoretical Chemistry
  • Computational Chemistry

Background:

  • Accurate representation of coupled electronic states is crucial for understanding molecular dynamics and spectroscopy.
  • Constructing quasidiabatic Hamiltonians is essential for simplifying complex quantum mechanical problems.
  • Previous methods faced limitations in accuracy and the range of applicability.

Purpose of the Study:

  • To develop a self-consistent procedure for constructing a quasidiabatic Hamiltonian for N coupled electronic states.
  • To improve the accuracy and extend the domain of applicability of diabatic Hamiltonians.
  • To incorporate point group symmetry and hermiticity into the Hamiltonian construction.

Main Methods:

  • Utilizes a crude adiabatic basis and analytic gradient techniques to determine linear term coefficients.
  • Employs the normal form of pseudolinear equations with ab initio data over an extended nuclear configuration range.
  • Applies a least-squares fitting approach to an overcomplete dataset for robust coefficient determination.

Main Results:

  • The developed method provides a quasidiabatic representation that minimizes residual derivative coupling in a least-squares sense.
  • Demonstrates the ability to extend the accuracy domain or refine accuracy within a given domain.
  • Successfully illustrated the method's attributes using the 1(2)A(1) and 1(2)E states of the 1-propynyl radical (CH(3)CC).

Conclusions:

  • The new procedure offers a robust and accurate method for constructing quasidiabatic Hamiltonians.
  • The approach enhances the reliability and applicability of theoretical models in chemical dynamics.
  • This work provides a significant advancement in the theoretical treatment of electronically coupled systems.