54.2 The VMCSCF program (VMCSCF)


The VMCSCF program is still under development and has not yet been fully optimized with respect to speed and efficiency. It is strongly recommended to run a VSCF calculation prior to the VMCSCF calculation and thus to use VSCF modals as an initial guess. By default configuration-selective VMCSCF calculations will be performed. The polynomial based VMCSCF calculation is significantly faster than the grid-based version and should be used whenever possible. For details see:

S. Heislbetz, G. Rauhut, Vibrational multiconfiguration self-consistent field theory: Implementation and test calculations, J. Chem. Phys. 132 (2010) 124102.
S. Heislbetz, F. Pfeiffer, G. Rauhut, Configuration selection within vibrational multiconfiguration self-consistent field theory: Application to bridged lithium compounds, J. Chem. Phys. 134 (2011) 204108.

The following options are available:

Is the number of active modals for each mode. The smallest meaningful value for NACT is 3, which is the current default. Configurations will only be generated within this space. Note that there is no equivalent in the VMCSCF program to the closed and core orbitals in electronic structure theory.
Is the number of modals on top of the number of active modals. The default is NVIRT=3. The virtual modals are needed for the modal rotations. Modals above the virtual modals are entirely neglected.
Specifies, if only active-virtual modal rotations shall be considered (ROT=0, default) or if active-active modal rotations shall be considered as well (ROT=1). Formally one would need active-active modal rotations for configuration-selective VMCSCF calculations, but the effects are usually extremely small.
The procedure how to determine the rotational angles between the modals within the Jacobi rotations can be specified by this keyword. CALCANGLE=1 uses the standard quadratic procedure, which is the current default. CALCANGLE=2 uses a cubic equation instead. CALCANGLE=3 switches to a full numerical determination of the rotational angle.
Once vibrational states have been defined with the VIBSTATE program (section 54.3), the VMCSCF program can be forced to compute just these states by the option USERMODE=1. Note that the vibrational ground state will always be computed and needs not to be specified explicitly.
By default configuration-selective VMCSCF calculations will be performed (VERSION=3). Note that the selection is always performed prior to the VMCSCF iterations but not within them. The selection of configurations can be switched off by (VERSION=4).
Defines the maximum number of simultaneous excitations within the configurations generated from modals of the active space, i.e. Singles, Doubles, Triples, ... The maximum excitation level is limited to CITYPE=6, the default is set to 4.
REF=0 specifies ground-state based VMCSCF calculations, i.e. the initial guess of the VMCSCF calculation is given by the VSCF wave function of the vibrational ground state. In contrast to that, REF=1 allows for a state-specific initial guess (default).
By default all VMCSCF calculations are based on state-specific VSCF modals, GSMODALS=0. GSMODALS=1 uses the modals of the VSCF ground-state for all VMCSCF calculations.
Controls the maximum number of macroiterations of the VMCSCF program. The default is 25.
Controls the convergence threshold for the macroiterations of the VMCSCF program. The default is 1.d-2.
Controls the maximum number of microiterations of the VMCSCF program. The default is 50.
Controls the convergence threshold for the microiterations of the VMCSCF program. The default is 1.d-5.
Provides additional information within the VMCSCF iterations, once a value larger than 0 (default) is used.
Specifies the record and file, on which the VMCSCF wave function shall be stored. The default is 5950.2.
Once set to 1, this option allows to store the VMCSCF modals in the record of the VSCF modals (which will be overwritten). This allows for VCI calculations with VMCSCF modals.

Besides these VMCSCF specific keywords, a number of option can be used, which are identical with those provided for the VCI program. These keywords are NDIM, VAM, TYPE, NBAS, DIPOLE, NDIMDIP, COMBI, INFO, MPG, DIAG, CONT, THRSEL, THRCF, ANALYZE.

molpro@molpro.net 2019-06-17