UV-Vis Absorption

Available Coupled Cluster Methods

• CCS

• PE-CCS

• CC2

• CCSD

• PE-CCSD

• CCSDT

Available Cluster Perturbation Methods

• CPS(D)

• CPSD(T)

Example Input File

An example input file for CCS takes the following form:

@method settings
basis: STO-3G
@end

@memory
max_mem: 1
@end

@jobs
task: ccs
@end

@ccs
restart: False
nstates: 3
spectrum: True
@end

@scf
conv_thresh: 1.0E-12
@end

@molecule
charge: 0
multiplicity: 1
units: bohr
xyz:
O        0.0000000000    0.0000000000    0.0000000000
H        0.0000000000    1.4304281903    1.1071565216
H        0.0000000000   -1.4304281903    1.1071565216
@end

Relevant Keywords

nstates
Description	Number of singlet excitation energies to calculate.
Type	int
Default	0

david_thresh
Description	Convergence threshold for the Davidson solver.
Type	float
Default	1.0E-6

spectrum
Description	Calculation of dipole oscillator strengths.
Type	bool
Default	False
Availability	CCS PE-CCS CC2 CCSD PE-CCSD

ntrips
Description	Number of triplet excitation energies to calculate.
Type	int
Default	0
Availability	CCS

cvs
Description	Calculate core excitations using core-valence separation (CVS).
Type	bool
Default	False
Availability	CCS

nactivecores
Description	Number of active cores in the CVS calculation.
Type	int
Default	1
Availability	CCS

rootwise
Description	Perform a pre-optimization of the excitation energies using the Davidson algorithm and converge each individual excitation energy using the DIIS/CROP algorithm.
Type	bool
Default	False

preopt_thresh
Description	Threshold for the Davidson algorithm used as pre-conditioner for the rootwise solver.
Type	float
Default	1.0E-4

max_reduced_space
Description	Maximal size of the reduced space in the Davidson solver. If this value is exceeded, the construction of the reduced space is restarted from the current eigenvectors.
Type	int
Default	8 × nstates / ntrips