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Variance-based wave function optimization within the unrestricted doubly occupied configuration interaction

Javier Garcia1, Diego R Alcoba2,3, Alicia Torre4

  • 1Instituto de Física La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, and Departamento de Física, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina.

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This study introduces a half-projection technique to reduce spin contamination in N-electron wave functions calculated with the unrestricted doubly occupied configuration interaction method. This method enhances the accuracy of electronic structure calculations for strongly correlated systems.

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Area of Science:

  • Quantum Chemistry
  • Computational Physics
  • Electronic Structure Theory

Background:

  • Energy-variance-based optimization is crucial for describing N-electron spectra.
  • Unrestricted doubly occupied configuration interaction (UDOCI) methods often yield wave functions with spin-contaminant contributions.
  • Spin contamination can affect the accuracy of calculated electronic properties.

Purpose of the Study:

  • To reduce spin contamination in wave functions obtained from the energy variance minimization version of the unrestricted doubly occupied configuration interaction method.
  • To implement and analyze the effectiveness of the half-projection technique within the UDOCI framework.
  • To identify the most suitable half-projection procedure for accurate electronic structure calculations.

Main Methods:

  • Incorporation of the half-projection technique into the unrestricted doubly occupied configuration interaction (UDOCI) framework.
  • Analysis of different implementation strategies for the half-projection method.
  • Numerical calculations on selected strongly correlated N-electron systems in both ground and excited states.

Main Results:

  • The proposed half-projection technique effectively reduces spin contamination in UDOCI wave functions.
  • Different implementation pathways of the half-projection method exhibit varying degrees of success.
  • Numerical results demonstrate the performance of the method across different electronic systems and states.

Conclusions:

  • The half-projection technique offers a viable solution to mitigate spin contamination in UDOCI calculations.
  • The study identifies optimal procedures for applying half-projection, improving the reliability of electronic structure predictions.
  • This work advances the accuracy of computational methods for strongly correlated electron systems.