.. index:: single: Program; CPF single: CPF single: MCPF single: ACPF .. _TUT\:sec\:cpf: :program:`CPF` --- A Coupled-Pair Functional Program ==================================================== The :program:`CPF` program produces Single and Doubles Configuration Interaction (SDCI), Coupled-Pair Functional (CPF), Modified Coupled-Pair Functional (MCPF), and Averaged Coupled-Pair Functional (ACPF) wave functions (see CPF section of the user's guide) from one reference configuration. The difference between the :program:`MRCI` and :program:`CPF` codes is that the former can handle Configuration Interaction (CI) and Averaged Coupled-Pair Functional (ACPF) calculations with more than one reference configuration. For a closed-shell reference the wave function can be generated with the :program:`SCF` program. In open-shell cases the :program:`RASSCF` has to be used. The :kword:`TITLe` keyword behaviors in a similar fashion to the other |molcas| modules. The :kword:`CPF` keyword requests an Coupled-Pair Functional calculation. This is the default and is mutually exclusive with keywords :kword:`MCPF`, :kword:`ACPF`, and :kword:`SDCI` which request different type of calculations. The input below lists the input files for the :program:`guga` and :program:`cpf` programs to obtain the MCPF energy for the lowest triplet state of :math:`B_2` symmetry in the water molecule. The :program:`GUGA` module computes the coupling coefficients for a triplet state of the appropriate symmetry and the :program:`CPF` module will converge to the first excited triplet state. One orbital of the first symmetry has been frozen in this case (core orbital) in the :program:`MOTRA` step. :program:`cpf` Output --------------------- The :program:`cpf` section of the output lists the number of each type of orbital in each symmetry including pre-frozen orbitals that were frozen by the :program:`guga` module. After some information concerning the total number of internal configurations used and storage data, it appears the single reference configuration in the :program:`mrci` format: an empty orbital is listed as "``0``" and a doubly occupied as "``3``". The spin of a singly occupied orbital by "``1``" (spin up) or "``2``" (spin down). The molecular orbitals are listed near the end of the output. Sample input requested by the GUGA and CPF modules to calculate the MCPF energy for the lowest :math:`B_1` triplet state of the water in :math:`C_{2v}` symmetry: :: &GUGA Title= H2O molecule. Triplet state. Electrons= 8; Spin= 3 Inactive= 2 0 1 0; Active= 1 1 0 0 CiAll= 2 &CPF Title= MCPF of triplet state of C2v Water MCPF There are four input files to the :program:`cpf` module; :file:`CIGUGA` from :program:`GUGA`, :file:`TRAONE` and :file:`TRAINT` from :program:`MOTRA` and :file:`ONEINT` from :program:`SEWARD`. The orbitals are saved in :file:`CPFORB`.