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## CASSCFCASSCF calculations can be performed with CFOUR via
Full CI calculations, with and without Frozen Core, can be also performed using the CASSCF module via
At the moment, only the CASSCF energy can be computed. The CASSCF module requires additional input, in particular, the user needs to specify the active space and how many alpha and beta electrons are to be correlated. The CASSCF input is given via an additional %casscf section which contains the following information - number of alpha/beta electrons and number of orbitals The number of active electrons and orbitals is specified by three integers separated by a space and given in the order - after running a HF calculation, the active orbitals can be given by providing a list of orbital numbers, as printed after the SCF has converged (in energy order). If an unrestricted calculation is performed, the alpha orbitals are to be used to specify the active space.
- by specifying the keyword CAS_INPUT=OCCUPATION, the active space can be defined by providing the number of
**internal**orbitals per irrep and, on a different line, the number of**active**orbitals per irrep.
As an example, we consider the SCF results for the OH ORBITAL EIGENVALUES (ALPHA) (1H = 27.2113838 eV) MO # E(hartree) E(eV) FULLSYM COMPSYM ---- -------------------- -------------------- ------- --------- 1 1 -19.9311866358 -542.3551695258 SG+ A1 (1) 2 2 -0.7546487737 -20.5350374298 SG+ A1 (1) 3 3 -0.0982048749 -2.6722905436 SG+ A1 (1) 4 8 -0.0026260430 -0.0714582650 PI B1 (2) 5 10 -0.0026260400 -0.0714581834 PI B2 (3) +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 6 4 0.6343389513 17.2612406758 SG+ A1 (1) 7 5 1.5405378884 41.9201677701 SG+ A1 (1) 8 9 2.2417638388 61.0014962509 PI B1 (2) 9 11 2.2417638422 61.0014963424 PI B2 (3) 10 6 2.4059031203 65.4679532399 SG+ A1 (1) 11 7 3.2891549689 89.5024583010 SG+ A1 (1) The CASSCF input for a CAS(8,8) calculation (full valence CAS) on the anion can be given as either %casscf or, by adding the keyword CAS_INPUT=OCCUPATION, by %casscf Notice that the SCF orbitals are used as a guess. A calculation on the OH radical can be performed by using the same orbitals and the following input %casscf %casscf The convergence threshold for the CASSCF optimization can be specified using the |

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CFOUR is partially supported by the U.S. National Science Foundation.