31.2 Running MRCC

The MRCC program is invoked by the command

MRCC,options
directives

The available options summarized in Table 9. For a detailed description please refer to the MRCC manual of M. Kallay (file ''manual'' the mrcc directory)

In MOLPRO the method to be used can be given as a string (option METHOD=string). The available methods and the corresponding MRCC input parameters (see MRCC manual) as specified in Table 10.

Directives are usually not necessary, but the CORE, OCC, ORBITAL, MAXIT, directives work as in the MOLPRO CCSD program. In addition, the number of states can be given on a STATE directive and this has the same meaning as the EOM_NSTATES option.

Table 9: Options for MRCC

Option	Alias	Default value$^a$	Meaning
METHOD	CALC	CC(n)	Computational method. See Table 10.
EXCITATION	LEVEL	-1	Excitation level in cluster operator
RESTART_CC	RESTART	0	Restart option. If 1, restart with previous amplitudes.
DIRECTORY	DIR	'  '	Subdirectory in which MRCC runs
			(necessary for restart jobs)
EOM_NSING	NSING	-1	Number of excited singlet states in closed-shell case
EOM_NTRIP	NTRIP	0	Number of excited triplet states in closed-shell case
EOM_NSTATES	NDOUB	-1	Number of states in open shell case.
SYMM	SYMMETRY	-1	Symmetry of excited states
DENSITY	IDENS	0	Parameter for density calculation
HF		1	0 for UHF or ROHF, 1 for closed-shell
NACTO		0	Number of active occupied orbitals
NACTV		0	Number of active virtual orbitals
SACC		0	Spin-adapted coupled cluster
DBOC		0	Diagonal BO correction
MEMORY		-1	Memory
TOL	ENERGY	-1.0	Energy convergence threshold
FREQ		0.0	Frequency for dynamic polarizabilities
FILE		fort	Name for MRCC fortran files
CONVER	ICONV	0	See mrcc manual
CS		1	See mrcc manual
DIAG		0	See mrcc manual
MAXEX		0	See mrcc manual
SPATIAL		1	See mrcc manual
a) -1 means default value taken from MOLPRO

Table 10: Methods available in the MRCC program

		MRCC parameters
	Key	METHOD	LEVEL	Notes
CI(n) configuration interaction methods
	CISD	0	2
	CISDT	0	3
	CISDTQ	0	4
	CI(N)	0	N	Specify excitation level N using LEVEL
CC(N) coupled cluster methods
	CCSD	1	2
	CCSDT	1	3
	CCSDTQ	1	4
	CC(N)	1	N	Specify excitation level N using LEVEL
CC(N-1)[N] coupled cluster methods
	CCSD[T]	2	3
	CCSDT[Q]	2	4
	CC(N-1)[N]	2	N	Specify excitation level N using LEVEL
CC(N-1)(N) coupled cluster methods. Also computes [n] corrections
	CCSD(T)	3	3
	CCSDT(Q)	3	4
	CC(N-1)(N)	3	N	Specify excitation level N using LEVEL
CC(n-1)(n)_L methods (also computes (n) and [n] corrections)
	CCSD(T)_L	4	3
	CCSDT(Q)_L	4	4
	CC(N-1)(N)_L	4	N	Specify excitation level N using LEVEL
CC(n)-1a methods
	CCSDT-1A	5	3
	CCSDTQ-1A	5	4
	CC(N)-1A	5	N	Specify excitation level N using LEVEL
CC(n)-1b methods
	CCSDT-1B	6	3
	CCSDTQ-1B	6	4
	CC(N)-1B	6	N	Specify excitation level N using LEVEL
CCn methods (only for ground states)
	CC3	7	3
	CC4	7	4
	CCN	7	N	Specify excitation level N using LEVEL
CC(n)-3 methods
	CCSDT-3	8	3
	CCSDTQ-3	8	4
	CC(N)-3	8	N	Specify excitation level N using LEVEL

Examples: Closed-shell ground-state calculations for H2O:

Input: h2o_mrcc.com

Output: h2o_mrcc.out

This yields

 METHOD                 E
 CC3                -76.23912734
 CCSD(T) (MOLPRO)   -76.23905150
 CCSD(T) (MRCC)     -76.23905150
 CCSDT              -76.23922746
 CCSDT(Q)           -76.23976632
 CCSDTQ             -76.23973043

Excitation energies for H2O:

Input: h2o_mrcc_eom.com

Output: h2o_mrcc_eom.out

This yields

 METHOD   PROG    STATES       E             EXC
 CCSD     MOLPRO     1.1   -76.23580212    0.000
 CCSD     MRCC       1.1   -76.23580212    0.000
 CCSDT    MRCC       1.1   -76.23922746    0.000
 CCSD     MOLPRO     1.2   -76.23580212    0.000
 CCSD     MRCC       1.2   -76.23580212    0.000
 CCSDT    MRCC       1.2   -76.23922746    0.000
 CCSD     MOLPRO     1.3   -76.23580212    0.000
 CCSD     MRCC       1.3   -76.23580212    0.000
 CCSDT    MRCC       1.3   -76.23922746    0.000
 CCSD     MOLPRO     1.4   -76.23580212    0.000
 CCSD     MRCC       1.4   -76.23580212    0.000
 CCSDT    MRCC       1.4   -76.23922746    0.000
 CCSD     MOLPRO     2.1   -75.85033256   10.489
 CCSD     MRCC       2.1   -75.85033257   10.489
 CCSDT    MRCC       2.1   -75.85316687   10.505
 CCSD     MOLPRO     2.2   -75.95093334    7.752
 CCSD     MRCC       2.2   -75.95093335    7.752
 CCSDT    MRCC       2.2   -75.95299013    7.789
 CCSD     MOLPRO     2.3   -75.77630664   12.504
 CCSD     MRCC       2.3   -75.77630665   12.504
 CCSDT    MRCC       2.3   -75.77972816   12.504
 CCSD     MOLPRO     2.4   -75.87776149    9.743
 CCSD     MRCC       2.4   -75.87776150    9.743
 CCSDT    MRCC       2.4   -75.88051189    9.761

Open-shell ground-state calculations for O2:

Input: o2_mrcc.com

Output: o2_mrcc.out

This yields

 METHOD                 E
 UCCSD(T) MOLPRO   -149.9815472
 RCCSD(T) MOLPRO   -149.9812566
 CCSDT MRCC        -149.9816705
 CCSDT MRCC        -149.9832255