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New algorithms accelerate the calculation of electronic states using equation-of-motion coupled-cluster (EOM-CC) methods. These novel computational approaches, including Davidson and GPLHR solvers, improve efficiency for quantum chemistry problems.

Keywords:
coupled-clusterdiagonalization algorithmseigensolversequation-of-motionexcited statesharmonic Ritz probleminterior eigenstates

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Theoretical Chemistry

Background:

  • Iterative diagonalization is crucial for solving large matrices in quantum chemistry.
  • Equation-of-Motion Coupled-Cluster (EOM-CC) methods are widely used for electronic structure calculations.
  • Efficient algorithms are needed to compute specific electronic states.

Purpose of the Study:

  • To introduce novel iterative diagonalization algorithms for electronic structure calculations.
  • To enhance the efficiency of computing low and high-lying ionized and electronically excited states.
  • To implement and evaluate new solvers within the Q-Chem electronic structure program.

Main Methods:

  • Development of two new algorithms for interior eigenvalue problems.
  • Implementation of a modified Davidson algorithm for specific transition calculations.
  • Utilizing Equation-of-Motion Ionization Potential Coupled-Cluster with Single and Double substitutions (EOM-IP-CCSD) and Equation-of-Motion Electron Equation Coupled-Cluster with Single and Double substitutions (EOM-EE-CCSD) methods.

Main Results:

  • The performance of the new algorithms was demonstrated through calculations of electronic states.
  • Two solvers, Davidson and Generalized Preconditioned Locally Harmonic Residual (GPLHR) method, were presented for excited state calculations.
  • A modified Davidson procedure was developed for targeted transition calculations.

Conclusions:

  • The new algorithms offer improved performance for EOM-CC calculations.
  • The developed methods are implemented in the Q-Chem software for practical application.
  • These advancements contribute to more efficient computation of electronic properties in molecules.