Ubuntu Manpage: ccenergy - Coupled cluster singles and doubles energy program

NAME

       ccenergy - Coupled cluster singles and doubles energy program

DESCRIPTION

       The  program ccenergy solves the coupled cluster singles and doubles amplitude equations.  This code will
       work for spin-restricted closed-shell Hartree-Fock (RHF), spin-restricted open-shell Hartree-Fock (ROHF),
       spin-unrestricted Hartree-Fock (UHF), and Brueckner references.   The  algorithm  makes  use  of  spatial
       symmetry  (D2h and its subgroups) and matrix algebra techniques for efficiency.  In addition, the program
       can be used to simulate local correlation methods.

REFERENCES

       1.     An introduction to coupled cluster theory for  computational  chemists,  T.D.  Crawford  and  H.F.
              Schaefer, Rev. Comp. Chem.  14 33-136 (2000).

       2.     A  direct product decomposition approach for symmetry exploitation in many-body methods. I. Energy
              calculations, J.F. Stanton, J. Gauss, J.D. Watts, and R.J.  Bartlett,  J.  Chem.  Phys.   94  4334
              (1991).

INPUT FORMAT

Input for this program is read from the file input.dat. The following keywords are valid:

WFN = string
Specifies the type of coupled cluster calculation desired. Valid entries at present are CCSD,
CCSD_T, BCCD, and BCCD_T. There is no default.

REFERENCE = string
Specifies the type of orbitals used for the single-determinant reference function. Valied entries
at present are RHF, UHF, and ROHF. There is no default.

MEMORY = (real MB)
The maximum amount of core memory to be used, in megabytes. See also the CACHETYPE and CACHELEV
keywords below.

CONVERGENCE = integer
Convergence desired on the CC amplitudes. Convergence is achieved when the RMS of the error in
the CC wave function is less than 10**(-n). The default is 7.

BRUECKNER_CONV = integer
Convergence desired for the orbitals in Brueckner-CC calculations. Convergence is achieved when
the largest absolute value of a single T1 ampltiudes is is less than 10**(-n). The default is 5.

MAXITER = integer
Maximum number of iterations to solve the coupled cluster equations. Defaults to 50.

FREEZE_CORE = string
Specifes whether core orbitals should be automatically frozen in the CC wave function. If this
option is set (preferably in the "default" section of input), then the cscf program will identify
the core orbitals. Subsequent codes starting with transqt will freeze these orbitals. Note that
this keyword usually makes the additional specification of FROZEN_DOCC unnecessary, but it may
still be required in some special cases. Allowed values are true, false, yes, no, 1, 0, large and
small.

FROZEN_DOCC = integer_array
The number of lowest energy doubly occupied orbitals in each irreducible representation from which
there will be no excitations. The Cotton ordering of the irredicible representations is used.
The default is the zero vector. NB: This keyword is actually read by the integral transformation
program transqt and the integral sorting program ccsort. See also the FREEZE_CORE keyword.

FROZEN_UOCC = integer_vector
The number of highest energy unoccupied orbitals in each irreducible representation into which
there will be no excitations. The default is the zero vector. NB: This keyword is actually read
by the integral transformation program transqt and the integral sorting program ccsort.

PRINT = integer
Determines the verbosity of the output. A value of 0 (the default) specifies minimal printing and
a value of 2 will give output updates as each term of the CC equations is complete. No other
values have yet been used.

NUM_AMPS = integer
Specifies the number of largest T1 and T2 amplitudes to print at the end of the CC procedure.
Default is 10.

PRINT_MP2_AMPS = boolean
Indicates if the MP2 amplitudes (which are starting guesses for RHF and UHF reference functions)
should be printed. Default is false.

RESTART = boolean
Allows the program to use old T1 and T2 vectors from previous calculations as the initial guesses
for a new calculation. This is particularly useful for geometry optimizations. The default is
TRUE. NB: The ability to restart a calculation is also controlled by the phases of the molecular
orbitals. If the parameter PHASE from the chkpt file (cf. libchkpt) is set to FALSE, then the
user's RESTART input will be ignored. This behavior can be overridden, however with the
FORCE_RESTART option.

FORCE_RESTART= boolean
Forces possible restart of the CC equations from previous T1 and T2 amplitudes. This option
should be used only by experts.

AO_BASIS= string
Compute contributions from four virtual-index integrals, <ab|cd>, from the atomic-orbital basis
integrals. This option slows the calculation somewhat, but greatly reduces disk-space
requirements. Allowed values are NONE (default), DISK (use the AO-basis integrals stored on
disk), or DIRECT (use cints to compute the AO-integrals on the fly in each CC iteration). The
DIRECT option is still experimental and should be used only by experts.

CACHETYPE= string
Selects the priority type for maintaining the automatic memory cache used by the DPD codes. (See
libdpd.html for further details.) A value of LOW (the default) selects a "low priority" scheme in
which the deletion of items from the cache is based on pre-programmed priorities. A value of LRU
selects a "least recently used" scheme in which the oldest item in the cache will be the first one
deleted.

CACHELEV= integer
Selects the level of automatic cacheing desired in the storage of various amplitudes, integrals,
and intermediates in the coupled cluster procedure. A value of 0 retains no quantities in cache,
while a level of 6 attempts to store all quantities in cache. For particularly large
calculations, a value of 0 may help with certain types of memory problems. The default is 2,
which means that all four-index quantites with up to two virtual-orbital indices (e.g., <ij|ab>
integrals) may be held in the cache.

DIIS= boolean
Selects the use of the direct-inversion in the iterative subspace (DIIS) technique of Pulay for
convergence acceleration. The default is TRUE.

LOCAL= boolean
Simluate the effects of local correlation techniques. The default is FALSE.

LOCAL_CUTOFF= real
The tolerance value (always between one and zero) for the Broughton-Pulay completeness check used
to contruct orbital domains for local-CC calculations. The default is 0.02. See J. Broughton and
P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104,
6286-6297 (1996).

LOCAL_METHOD= string
Selects the type of local-CCSD scheme to be simulated. Valid entries are WERNER for the method
develop by H.-J. Werner and co-workers or AOBASIS for the method developed by G.E. Scuseria and
co-workers (currently inoperative). The default is WERNER.

LOCAL_WEAKP= string
Selects the desired treatment of "weak pairs" in the local-CCSD method. A value of NEGLECT
ignores weak pairs entirely. A value of NONE treats weak pairs in the same manner as strong
pairs. A value of MP2 (the default) uses second-order perturbation theory to correct the local-
CCSD energy computed with weak pairs ignored.

PRINT_PAIR_ENERGIES = boolean
Indicates if the MP2 and CCSD pair energies should be printed. This is only possible for RHF
references. Default is false.

SPINADAPT_ENERGIES = boolean
Indicates if spin-adapted pair energies should be printed. Default is false.

18 June, 2002 ccenergy(1)