Effective Hamiltonians From Correlated Wavefunctions

Effective Hamiltonians deliver physical insights from the complicated many-body Hamiltonians. Q-Chem’s effective Hamiltonian implementations offer a straightforward and rigorous way to extract model Hamiltonian parameters from high-level correlated wavefunctions, enabling studies of magnetic properties in large systems.

• Useful and intuitive physical insights into magnetic couplings;

• Straightforward extraction of model Hamiltonian parameters for multi-site systems;

• Direct comparison between ab initio and experimental coupling parameters;

• Model Hamiltonians enable calculations of an entire low-energy manifold of states in large strongly correlated systems from just one inexpensive single spin-flip calculation;

• Q-Chem offers effective Hamiltonian extractions for two types of correlated wavefunctions:

  • EOM-SF-CCSD Effective Hamiltonian

    • Based on highly accurate coupled-cluster wavefunctions;

    • Parameter extraction for Heisenberg and Hubbard model Hamiltonians;

    • Available in Hermitian (Bloch) and non-Hermitian (des Cloizeaux) formulations.

  • RAS(h,p)-1SF Effective Hamiltonian

    • Parameter extraction for Heisenberg Hamiltonian;

    • Enables studies on large high-spin systems with multiple orbitals per site.