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Time-dependent projected Hartree-Fock.

Takashi Tsuchimochi1, Troy Van Voorhis1

  • 1Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA.

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This summary is machine-generated.

Projected Hartree-Fock (PHF) methods accurately describe excited states in degenerate systems. These new time-dependent equations offer improved accuracy over traditional TDHF, even for complex molecules.

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Area of Science:

  • Quantum Chemistry
  • Computational Physics
  • Theoretical Chemistry

Background:

  • Static correlation in degenerate systems poses challenges for traditional quantum chemistry methods.
  • Projected Hartree-Fock (PHF) offers a promising alternative for describing such systems.
  • Accurate calculation of excited states is crucial for understanding molecular properties and reactions.

Purpose of the Study:

  • To derive and implement linearized time-dependent equations for Projected Hartree-Fock (TDPHF).
  • To enable the calculation of excited states using the PHF formalism.
  • To benchmark the performance of TDPHF against time-dependent Hartree-Fock (TDHF).

Main Methods:

  • Derivation of linearized time-dependent equations for PHF (TDPHF).
  • Analysis of the connection between TDPHF and PHF wave function stability.
  • Benchmarking using TDPHF with spin-projection (TDSUHF) and its Tamm-Dancoff approximation on various molecules.

Main Results:

  • TDPHF and TDSUHF provide consistently better descriptions of excited states than TDHF for degenerate molecules.
  • The methods naturally yield both singly and doubly excited states due to spin-projection.
  • While singly excited states of PHF show size-extensivity issues, doubly excited states remain accurate at the thermodynamic limit.

Conclusions:

  • Linear-response TDPHF is a robust method for calculating excited states in systems with static correlation.
  • The developed methods offer superior accuracy compared to TDHF at similar computational costs.
  • TDPHF provides a valuable tool for studying excited-state properties of challenging molecular systems.