Multiconfiguration self-consistent field implementation

VI. Implementation of Multiconfiguration Self-consistent Field Methods... 

VI. IMPLEMENTATION OF MULTICONFIGURATION SELF-CONSISTENT FIELD METHODS... 

For the MFP approach, most calculations have used SCF wavefunctions. However, very recently, Bak et al. have implemented the MFP theoretical approach at the correlated multiconfigurational self-consistent-field level by using the complete active space wavefunctions (CASSCF) expressed over conventional and gauge invariant basis sets. 

Heislbetz S, Rauhut G (2010) Vibrational multiconfiguration self-consistent field theory Implementation and test calculations. J Chem Phys 132 124102... 

Malmqvist P-A, Rendell A, Roos BO. The Restricted Active Space Self-Consistent-Field Method, Implemented with a Split Graph Unitary Group Approach. J Phys Chem. 1990 (4). Ma D, Li Manni G, Gagliardi L. The generalized active space concept in multiconfigurational self-consistent field methods. J Chem Phys [Internet]. 2011 Jul 28 [cited 2012 Mar 1] 135(4) 044128. Available from http //www.ncbi.nlm.nih.gov/pubmed/21806111. 

The various response tensors are identified as terms in these series and are calculated using numerical derivatives of the energy. This method is easily implemented at any level of theory. Analytic derivative methods have been implemented using self-consistent-field (SCF) methods for a, ft and y, using multiconfiguration SCF (MCSCF) methods for ft and using second-order perturbation theory (MP2) for y". The response properties can also be determined in terms of sum-over-states formulation, which is derived from a perturbation theory treatment of the field operator — [iE, which in the static limit is equivalent to the results obtained by SCF finite field or analytic derivative methods. 

The Valence Bond Self-Consistent Field (VBSCF) method has been devised by Balint-Kurti and van Lenthe (32), and was further modified by Verbeek (6,33) who also developed an efficient implementation in a package called TURTLE (11). Basically, the VBSCF method is a multiconfiguration SCF procedure that allows the use of nonorthogonal orbitals of any type. The wave function is given as a linear combination of VB structures, (Eq. 9.7). 

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