Four-component DSRG-MRPT2/3

This is a pilot implementation of a four-component multi-reference many-body perturbation theory based on the DSRG-MRPT2 (Driven Similarity Renormalization Group second-order Multi-Reference Perturbation Theory) formalism, based on a 4c-CASCI or 4c-CASSCF reference.

Current capabilities

• Interface to PySCF, specifically for the Dirac-Hartree-Fock solver and its interface to libcint for integrals. The DC integrals are density fitted, the DCG and DCB cannot be currently density fitted.
• NR/4C-DHF integral transformation
  • Ability to read in MO coefficients from other sources, specifically PySCF, Psi4 and ChronusQ, the latter enables using 4C-CASSCF references.
  • Density fitting is available throughout the code
  • Frozen core / deleted virtual approximations
• NR/4C-MP2
• NR/4C-CASCI solver
• NR/4C-DSRG-MRPT2/3, based on either (NR/4C-)CASCI or (NR/4C-)CASSCF references
  • Use of semicanonical orbitals
  • Full reference relaxation
  • State-averaging
• NR/4C Adaptive CI (ACI)
  • TD extension (TD-ACI) for ionized states.

To-dos

• Memory optimization
• State-averaged ACI