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21 MULTIREFERENCE RAYLEIGH SCHRÖDINGER PERTURBATION THEORY

Bibliography:

Original RS2/RS3:

H.-J. Werner, Mol. Phys. 89, 645-661 (1996)

New internally contracted RS2C:

P. Celani and H.-J. Werner, J. Chem. Phys. 112, 5546 (2000)

All publications resulting from use of this program must acknowledge the above.

The commands

RS2,options
RS2C,options
RS3,options

are used to perform second or third-order perturbation calculations. RS3 always includes RS2 as a first step. For closed-shell single-reference cases, this is equivalent to MP2 or MP3 (but a different program is used). RS2C calls a new more efficient second-order program (see below), which should normally be used if third-order is not required (note that RS3C is not available).

for RS2 an explicitly correlated version as described in T. Shiozaki and H.-J. Werner, J. Chem. Phys. 133, 141103 (2010) is available. This is called using the command

RS2-F12, options

Options can be the following:

Gn
Use modified zeroth order Hamiltonian, see section 21.4
SHIFT=value
Level shift, see section 21.5
IPEA=value
IPEA shift proposed by G. Ghigo, B. O. Roos, and P.A. Malmqvist, Chem. Phys. Lett. 396, 142 (2004), see section 21.5.
MIX=nstates
Invokes multi-state (MS-CASPT2) treatment using nstates states. See section 21.3 for more details.
XMS=0:
MS-CASPT2 method of Finley et al. CPL 288, 299 (1998)
XMS=1:
Extended multi-state CASPT2 (XMS-CASPT2) method as described in J. Chem. Phys. 135, 081106 (2011). fully invariant treatment of level shifts (recommended).
XMS=2:
XMS-CASPT2 method; level shift is only applied to the diagonal of H0.
ROOT=ioptroot
Root number to be optimized in geometry optimization. This refers to the nstates included in the MS-CASPT2. See section 21.7 for more details.
SAVEH=record
Record for saving the effective Hamiltonian in MS-CASPT2 calculations. If this is not given, a default record will be used (recommended).
INIT
(logical) Initializes a MS-CASPT2 with single state reference functions, see section 21.3
IGNORE
(logical) Flags an approximate gradient calculation without CP-CASPT2; see section 21.7 for details.
In addition, all valid options for MRCI can be given (see Sect. 20).



Subsections

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