MOLCAS program

The MOLCAS program of Professor Bjorn Roos webpage teobor garm.teokem.lu.se A nice compendium of various softwares Is given In the appendix of reviews In ... 

Table 14.3 Computation times (in seconds) of various exact-decoupiing methods for the heavy ion Rn+ . m denotes the number of basis functions. Time ratios with respect to m=100 are given in parentheses. The data have been taken from Ret. [16], which describes the implementation in the Molcas program package [638], The results were obtained tor 128-bit precision on an Opteron 250 central processing unit. The evaluation of one-electron integrals was not included in the measurement of the computing time.

Regardless of whether a single- or multireference wavefunction is used for a CISD calculation, the effects of higher excitations (e.g., triples and quadruples) are obviously not included. Quadruple excitations are particularly important because it is their absence from CISD wavefunctions for closed-shell molecules that results in these wavefunctions not being size consistent. Methods for estimating the effect of quadruple excitations have been developed, both by Davidson and by Pople. The Davidson corrections for quadruples can easily be computed by hand, but they are also automatically calculated as part of the CISD modules in the MOLPRO and MOLCAS programs. 

Cl results can vary a little bit from one software program to another for open-shell molecules. This is because of the HF reference state being used. Some programs, such as Gaussian, use a UHF reference state. Other programs, such as MOLPRO and MOLCAS, use a ROHF reference state. The difference in results is generally fairly small and becomes smaller with higher-order calculations. In the limit of a full Cl, there is no difference. 

Molden (we tested Version 3.6) is a molecular display program. It can display molecular geometries read from a number of molecular file formats. Various views of the wave function can be displayed from the output of the Gaussian and GAMESS programs. Some functionality is available from MOP AC and AMP AC files. Conversion programs are available to import wave functions from ADF, MOLPRO, ACES II, MOLCAS, DALTON, Jaguar, and HONDO. 

Karlstrom G, Lindh R, Malmqvist P-A, Roos B, Ryde U, Veryazov V, Widmark P-O, Cossi M, Schimmelpfennig B, Neogrady P, Seijo L (2003) Molcas a program package for computational chemistry. Comput material sci 28 222... 

Ungur, L. and Chibotaru, L.F. (2006-2013) SINGLE ANISO Program, KU Leuven, Belgium, http //www.molcas.org (accessed 09 September 2014). 

The computational details concerning basis sets and geometries are given in the following section. The MOs have been calculated with the MOLCAS series of programs [44]. The (SC) -MR-SDCI have been calculated with the CASDI series of programs [41,45] as adapted to run on IBM RS/6000 workstations and on SGI multiprocessor computers. 

Several different versions of second-order perturbation theory for multireference wave functions have been implemented but the one currently in widest use is probably the CASPT2 method. This method was developed by Roos and co-workers in Lund, Sweden, and it is available in their MOLCAS package of computer programs. 

The most common quantum chemical programs—Gaussian (8), GAMESS (9), Turbomole (10), CADPAC (11), ACES II (12), MOLPRO (13), MOLCAS (14), and the newly developed TITAN (15)—are able to run pseudopotential calculations. Please note that CADPAC and MOLCAS can only use so-called ab initio model potentials (AIMPs) in pseudopotential calculations. Such AIMP differ from ECPs in the way that the valence orbitals of the former retain the correct nodal structure, while the lowest-lying valence orbital of an ECP is a nodeless function. Experience has shown that AIMPs do not give better results than ECPs, although the latter do not have the correct nodal behavior of the valence orbitals... 

Computer programs were MOLCAS 3 program system (25) for SCF, CASSCF, and CASPT2 calculations and the program TITAN for closed shell calculations (26). The new version of the COMENIUS program was used for open shell CCSD(T) calculations based on the spin adapted singly and doubly excited amplitudes (15, 27-29). These codes were supplemented by the generator of the no-pair hamiltonian written by B. A. Hess in all DK calculations. 

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