6 Wave Function-Based Correlation Methods

6.8 Coupled-Cluster Methods

The following sections give short summaries of the various coupled-cluster based methods available in Q-Chem, most of which are variants of coupled-cluster theory. The basic object-oriented tools necessary to permit the implementation of these methods in Q-Chem was accomplished by Profs. Anna Krylov and David Sherrill, working at Berkeley with Martin Head-Gordon, and then continuing independently at the University of Southern California and Georgia Tech, respectively. While at Berkeley, Krylov and Sherrill also developed the optimized orbital coupled-cluster method, with additional assistance from Ed Byrd. The extension of this code to MP3, MP4, CCSD and QCISD is the work of Prof. Steve Gwaltney at Berkeley, while the extensions to QCCD were implemented by Ed Byrd at Berkeley. The original tensor library and CC/EOM suite of methods are handled by the CCMAN module of Q-Chem. Recently, a new code (termed CCMAN2) has been developed in Krylov group by Evgeny Epifanovsky and others, and a gradual transition from CCMAN to CCMAN2 has begun. During the transition time, both codes will be available for users via the CCMAN2 keyword.

CORRELATION
       Specifies the correlation level of theory handled by CCMAN/CCMAN2.
TYPE:
       STRING
DEFAULT:
       None No Correlation
OPTIONS:
       CCMP2 Regular MP2 handled by CCMAN/CCMAN2 MP3 CCMAN and CCMAN2 MP4SDQ CCMAN MP4 CCMAN CCD CCMAN and CCMAN2 CCD(2) CCMAN CCSD CCMAN and CCMAN2 CCSD(T) CCMAN and CCMAN2 CCSD(2) CCMAN CCSD(fT) CCMAN and CCMAN2 CCSD(dT) CCMAN CCVB-SD CCMAN2 QCISD CCMAN and CCMAN2 QCISD(T) CCMAN and CCMAN2 OD CCMAN OD(T) CCMAN OD(2) CCMAN VOD CCMAN VOD(2) CCMAN QCCD CCMAN QCCD(T) CCMAN QCCD(2) CCMAN VQCCD CCMAN VQCCD(T) CCMAN VQCCD(2) CCMAN
RECOMMENDATION:
       Consult the literature for guidance.

Note:  All methods implemented in CCMAN2 can be executed in combination with the C-PCM implicit solvent model (section 7.8.11) and with the EFP method (section 12.5). Only energies and unrelaxed properties are available (no gradient).