Single-point Energy Calculations
Single-point energy calculations are possible at the following levels:
using closed-shell (RHF), open-shell (UHF), or restricted-open-shell (ROHF) reference functions. In addition,
and CC calculations using a QRHF reference function
are possible. At the MP2 level, also spin-component scaled MP2 (SCS-MP2) calculations can be carried out.
In the case of open-shell systems, besides the usual spin-orbital based CC scheme (using either UHF, ROHF, or QRHF reference functions) partially-spin-adapted and spin-restricted CC (PSA-CCSD and SR-CCSD) calculations are possible.
Furthermore, for the treatment of open-shell singlets, a two-determinant CC (TD-CC) scheme is provided.
CC and CI calculations using higher than triple excitations can be performed with the MRCC code by M. Kállay which has been interfaced to CFOUR (see Interface to MRCC). With this interface, calculations can be also performed using methods with an approximate treatment of higher excitations such as, for example, CCSDT(Q), CC4, etc.