COLUMBUS

COLUMBUS is a collection of programs for high-level ab initio molecular electronic structure calculations. The programs are designed primarily for extended multi-reference (MR) calculations on electronic ground and excited states of atoms and molecules.
An important feature of COLUMBUS is its flexibility. In addition to standard classes of reference wave functions, such as CAS or RAS, calculations can be performed with selected reference configurations. Though the multi-reference aspect of COLUMBUS is emphasized, single-reference calculations can also be carried out very efficiently.
Main features:
- SCF - closed-shell and restricted open-shell
- MCSCF - general MCSCF with quadratic convergence including state-averaging
- MR-CISD - direct CI for all single and double excitations from an arbitrary set of reference configurations
- MR-ACPF and MR-AQCC - modified MRCISD methods that include iterative size-extensivity corrections
- Analytic gradient for MCSCF, MR-CISD, MR-ACPF and MR-AQCC
- Analytic MR-CISD nonadiabatic coupling vector
- Automatic geometry optimization and saddle-point searches
- Automatic searches for minima on the crossing seam (conical intersections)
- Spin/orbit CI
- A massively-parallel version of the MR-CISD, MR-AQCC and respective two-electron density program sections.
Enhancements:
- Analytic MR-CISD/AQCC gradient for excited states based on state-averaged MCSCF calculations
- Analytic MR-CISD nonadiabatic coupling vector
- Automatic searches for minima and saddle points in excited states
- Automatic searches for minima on the crossing seam (conical intersections)
- Integration of the GUGA spin-orbit CI program (still in test phase)
- A massively parallel CI and two-electron density code
- Enhanced user interface including visualization features via MOLDEN.