A progress report on the status of the COLUMBUSMRCI program system

Abstract

The COLUMBUS program system is a collection of Fortran programs for performing general multireference single-and double-excitation configuration interaction (MRSLICI) wave function optimization based on the graphical unitary group approach. The program system also includes integral generation, SCF and MCSCF orbital optimization, integral transformation, and wave function analysis programs. The original program system was written in 1980 to 1981. Since that time, it has evolved into one of the most popular MRSDCI program systems used in the computational chemistry community. The discussion of this evolution will include the exploitation of efficient matrix-matrix and matrix-vector product computational kernels, the use of generally contracted symmetry-adapted orbital basis sets, general Hamiltonian diagonalization procedures, energy-based internal walk selection, flexible DRT specification, improved coupling-coefficient evaluation methods, coupled-pair functional and multireference CPF capabilities, and density matrix construction. The numerous versions of the program system that are maintained at different sites and on different computers are now in the process of being merged. The source code for this combined version will be made available to the computational chemistry community. The source code for a specific computer may be generated from the source code for another computer by a single pass through a simple filter utility that is included with the program system. The directly supported computers will initially include various models of VAX, Cray, FPS, IBM, CDC, and ETA machines with the addition of other machines shortly thereafter. The ongoing developments of the COLUMBUS system that are discussed include a new method for computing analytic energy gradients for MRSDCI wave functions. This effective-density-matrix based method avoids the "coupled perturbed MCSCF" solutions for each coordinate direction, avoids the transformation of any derivative-integral quantities from the AO to the MO basis, avoids the transformation of the coupling coefficients from the MO to the AO basis, allows a subset of the MCSCF doubly occupied orbitals to be frozen in the CI wave function, and allows the MRSLXI wave function to be generated from general reference CSFs that are not necessarily related to the MCSCF expansion CSFS.

Theoretical Study of the Reaction O(3P) + C2H4 and Comparison with the 3CH2 + C2H4 Reaction

“…The potential curve was calculated at the single-double CI (SD-CI) Ievel because multireference effects are not expected to be important for this distortion, using the COLUMBUS program package. 22 The present calculations predict the lowest energy at CZ, = 0° the energy maximum is found for an angle around 60°. The predicted barrier height is around S-6 kcal/mol.…”

Accurate elastic scattering factors for lithium to argon based on correlated wavefunctions

“…We thank Professor H. Lischka for helpful suggestions and for making the MR-SDCI gradient program (Shepard, Lischka, Szalay, Kovar & Ernzerhof, 1992) available to us. We are also grateful to Professor R. Shepard for providing us with the COLUMBUS program (Shepard et al, 1988). We gratefully acknowledge the computer time provided by the following institutions: HLRZ Jtilich GmbH (Cray Y-MP), Verbund der Hessischen H6chstleistungsrechner (SNI 100) and Rechenzentrum der Universitat Marburg (Convex C-230).…”

“…All electrons (valence and core electrons) were included in the correlation treatment. The MR-SDCI calculations were carried out using the COLUMBUS program (Shepard et al, 1988). The one-electron density matrix elements were computed by means of the MR-SDCI gradient program (Shepard, Lischka, Szalay, Kovar & Emzerhof, 1992).…”

Impact of electron–electron cusp on configuration interaction energies

“…In codes (e.g. the ARGOS code [31]) which use the Rys quadrature [25] approach for the evaluation of two-electron integrals with the Coulomb interaction, these Gaussian terms are already evaluated in an intermediate stage and may be used in the present context.…”