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Area of Science:

  • Quantum Chemistry
  • Theoretical Chemistry
  • Computational Chemistry

Background:

  • Complex absorbing potential (CAP) is a key method for characterizing electronic resonances in quantum mechanics.
  • Current CAP methods lack efficient tools for exploring resonance potential energy surfaces, such as geometry optimization.
  • Analytic nuclear gradients are limited to specific electronic structure methods for CAP-based calculations.

Purpose of the Study:

  • To develop a general approach for calculating nuclear gradients and nonadiabatic couplings for electronic resonances.
  • To extend the applicability of CAP methods to geometry optimizations and dynamical simulations of resonance states.
  • To enable the use of various electronic structure methods for resonance characterization.

Main Methods:

  • Utilized the projected complex absorbing potential (CAP) technique.
  • Extended bound-state gradients and nonadiabatic couplings to resonance states.
  • Applied the method to state-averaged complete active space self-consistent field (SA-CASSCF) and multireference configuration interaction with single excitations (MRCI) methods.

Main Results:

  • Developed a general approach for analytic nuclear gradients and nonadiabatic couplings for resonances.
  • Successfully applied the method to SA-CASSCF and MRCI electronic structure theories.
  • Reported accurate equilibrium geometries for temporary anions like N2-, H2CO-, HCOOH-, and C2H4-.

Conclusions:

  • The projected CAP technique provides a versatile framework for calculating resonance properties.
  • The developed method significantly enhances the capability for studying resonance phenomena in molecular systems.
  • This work paves the way for more detailed investigations of temporary anions and other resonance states.