ccq Coupled-Cluster Program

ccq is a coupled-cluster (CC) software package capable of running calculations with up to quadruply excited cluster components. This package includes the standard CCSD, CCSDT, and CCSDTQ approaches, the active-space CCSDt, CCSDtq, and CCSDTq methods, and the CR-CC(2,3) and CC(t;3) approaches based on the CC(P ; Q) hierarchy.

Building

A BLAS library is required to compile this program. It is strongly advised to use an optimized version, such as OpenBLAS or Intel's MKL.

To compile, just link or copy a configuration file in config/ to config.mk. Make sure that it contains the right configuration options (e.g. compilers, libraries, etc.)

For example:

ln -s config/gfortran.mk config.mk
make -j4

Input file

System information

The configuration file must include the following information for any calculation type

froz:

number of frozen spatial orbitals

nel:

number of electrons (occupied spin-orbitals)

nvir:

number of virtual orbitals (unoccupied spin-orbitals)

multiplicity:

spin multiplicity

onebody:

path to the onebody.inp integral file as provided by CC_PACKAGE

twobody:

path to the twobody.inp integral file as provided by CC_PACKAGE

Runtime options

tol:

energy convergence tolerance. Can be an integer, in which case tol=10^tol. The default value is 1.0E-4.

shift:

shift energy used to help converge certain difficult calculations. It's used at the end of each Jacobi iteration and shifts the denominator's value.

diis_space:

the size of the DIIS space. Default is 5.

max_iterations:

maximum number of iterations before exiting the calculation. Default is 60.

calc_type:

select calcualtion type. Currently the supported calculations are CCSD, CCSDT, CCSDTQ, CCSDt, CC(t;3), CADFCIQMC, and DCSD-MC.

label:

project label. Will be shown in the output. Useful to help identify the calculation.

num_threads:

number of threads to use in the shared-memory parallel sections (default is 1)

sym_file:

symmetry file containing the spatial symmetries of the molecular orbitals. The first value of the file is the point group (C1 is 1; C2v, 3; D2h, 4)

rhf:

force a closed-shell calculation (default is .false.)

Active space options

act_occ:

number of active occupied spatial orbitals

act_unocc:

number of active unoccupied spatial orbitals

act_ind_t:

number of active indices in a triply excited cluster

act_ind_q:

number of active indices in a quadruply excited cluster

ACC options

ACC options to scale various diagrams. All values are space separated.

t2t2_t2:

T_2^2 projected on doubles. Takes 5 values.

t3_t2:

T_3 projected on doubles. Takes 2 values.

t1t3_t2:

T_1 * T_3 projected on doubles. Takes 4 values.

t2t2_t3:

T_2^2 projected on triples. Takes 3 values.

t2t3_t3:

T_2 * T_3 projected on triples. Takes 5 values.