$GMCPT group (relevant if CISTEP=GMCCI in $MCSCF) (relevant if MRPT=GMCPT in $MRMP) This group specifies the determinants to be used in a general MCSCF wavefunction. Additional inputs give the necessary information to compute a 2nd order perturbation energy correction to the MCSCF energy of such a MCSCF reference, by choosing MPLEVL=2 in $CONTRL and MRPT=GMCPT. The PT is of quasidegenerate type, in which several MCSCF states can be perturbed simultaneously. After 2nd order correction to both its diagonal and off-diagonal matrix elements, this model Hamiltonian is diagonalized to give the GMC-QDPT energies. The diagonalization also yields some information about the remixing of the reference states at 2nd order. Of course, the program can also be used to obtain the 2nd order correction to the energy of just one state. GMC-QDPT is therefore analogous to the two equivalent MCQDPT programs (MRPT=MCQDPT or DETMRPT) for CAS-type references, but allows more general types of MCSCF reference. Compared to those programs, there are also choices for the 0-th order states, for the orbital energies, and for the treatment of external excitations. The letters GMCPT should be understood as standing for GMC-QDPT, and have been shortened only because of the constraints on input group names to 6 or fewer letters. At the present time, this program does not support EXETYP=CHECK. It is enabled for parallel execution. 1. data to specify active space and electronic state: NMOFZC: number of frozen core orbitals, during the PT the shape of these orbitals will be optimized in the MCSCF stage, so they are "frozen" in the sense of not being correlated in the PT. The default is the number of chemical core orbitals. NMODOC: number of orbitals restricted to double occupancy during MCSCF, but which are correlated in the PT calculation. In other words, the filled valence orbitals. (no default). (It is possible to enter a different keyword NMOCOR which is the total number of doubly occupied orbitals, and NMOFZC. In this case the program will obtain NMODOC by subtraction, namely NMODOC = NMOCOR - NMOFZC). NMOACT: number of active orbitals in the MCSCF (no default) NMOFZV: number of virtual orbitals to be omitted from the PT step. The default is 0, retaining all virtuals. NELACT: number of active electrons. Since the default is computed from the total number of electrons given in $DATA and $CONTRL's ICHARG, minus 2*NMOFZC minus 2*NMODOC, there is little reason to input this. MULT: multiplicity of the state, with the default being taken from MULT in $CONTRL. SZ: spin projection quantum number for determinants, default is (MULT-1)/2 STSYM: The symmetry of the electronic state. See $DET for possible values: use AP/APP in Cs, not primes. Default is the totally symmetric representation. If you are treating a system with degenerate states in an appropriate Abelian subgroup of the true group, up to three STSYM values can be given, to specify all components of that originally degenerate state. For example, STSYM(1)=b1u,b2u,b3u generates all P states for an atom running in the Abelian subgroup D2h. 2. data to specify the MCSCF CI (and PT's reference CI): The type of general MCSCF reference is specified by REFTYP, which can be MRX, ORMAS, or RAS: REFTYP= MRX means multi-reference determinant list, plus excitations (default). The determinants will be given by $PDET input, and the keywords NPDET and NEXCIT defined below are required. REFTYP= RAS means the active space is divided into three subspaces, known as RAS1, RAS2, and RAS3. Keywords MSTART and NEXCIT defined below are required. For example, MSTART(1)=4,6,9 defines a RAS with three orbitals in the NMOFZC/NMODOC spaces, while the RAS1, RAS2, and RAS3 subspaces contain 2, 3, and NMOACT-5 orbitals. It remains only to specify the excitation level NEXCIT between these spaces. REFTYP= ORMAS defines even more general subspaces than RAS, and requires inputs NSPACE, MSTART, MINE, and MAXE. These have the same meaning as the $ORMAS keywords. NPDET is the number of parent determinants, to be given as NPDET lines in the $PDET input. A value is required for REFTYP=MRX. NEXCIT is an excitation level. A value is required for REFTYP=MRX or REFTYP=RAS. NSPACE is the number of subspaces into which the active space is divided. Required for REFTYP=ORMAS. MSTART is an array telling the starting MO of each orbital space. It is required for REFTYP=RAS and ORMAS. MINE is an array giving the minimum number of electrons occupying each subspace. Required for REFTYP=ORMAS. MAXE is an array giving the maximum number of electrons occupying each subspace. Required for REFTYP=ORMAS. NSPACE, MSTART, MINE, and MAXE have the same meaning as in the $ORMAS input. See the 'how to do MCSCF/CI' section of REFS.DOC, for help in understanding the power of the ORMAS type of reference determinant list. 3. data to define the reference CI states: KSTATE is an array of states to be used. As an example, KSTATE(1)=0,1,0,1 means use states 2 and 4. The default is the ground state, KSTATE(1)=1,0,0... WSTATE is a set of weights for each state. The default is equal weight assigned to every state selected by KSTATE (WSTATE(1)=1.0, 1.0, 1.0, ...) IROOT specifies which state's energy should be saved for use in numerical gradient evaluation. IROOT counts only for those states included by KSTATE, so KSTATE(1)=0,1,0,1 and IROOT=2 refers to the second root computed (4th overall). Default: IROOT=1. ISPINA spin adaptation (default=0) 0 means off, 1 means on (strictly), -1 means on (loosely). Proper spin states are picked up automatically so this input is usually skipped. See NSOLUT in this context. KNOSYM a flag to turn off space symmetry use, i.e. STSYM. .FALSE. will ignore symmetry (default=.TRUE.) KNOSPN a flag to ignore spin symmetry, i.e. MULT. Give as .FALSE. to ignore the spin (default=.TRUE.) The next few influence the Davidson CI diagonalization, and are quite similar to $MCQDPT keywords, so the description here is terse. NSOLUT is the number of roots to be obtained. If there are not enough states of the correct spin found in the first NSOLUT states to satisfy KSTATE/WSTATE, increase this parameter to find enough. MXITER is the maximum number of Davidson iterations to find the states (default=200) THRCON is the convergence criterion on the CI coefficient convergence (default= 1.0d-6) THRENE is a convergence criterion on the total energy of the states. This is ignored if given as a negative number. (default = -1.0d-12 Hartree) MAXBAS maximum expansion space size in the Davidson diagonalization subspace (default=100) MDI dimension of the initial guess subspace used to initiate the Davidson iterative CI solver. See NHGSS in $DET for more information (default=300). 4. data to define perturbation theory computation: KXGMC a flag to choose the 0-th order Hamiltonian used, when more than one state is included by KSTATE and WSTATE. KXGMC has no impact on single state runs. .TRUE. selects Granovsky's XMCQDPT equations for the zero-th order Hamiltonian, see A.A.Granovsky, J.Chem.Phys. 134, 214113(2011). .FALSE. selects the original definition of the unperturbed Hamiltonian. The default is .TRUE. IWGT selects wavefunction analysis (default=1) 0 means off, 1 means on (external), -1 means on (internal orbitals). This will compute the approximate weight of the MCSCF reference CI in the first order wavefunction. It is therefore a very useful diagnostic for the quality of the calculation, as the MCSCF state should be a high percentage. The formula for the decomposition is changed from the original CAS-type MCQDPT (REFWGT in $MCQDPT), see Miyajima, Watanabe, and Nakano's reference cited below. Select IWGT=0 if the fastest speed is desired. KFORB flag to request canonicalization (default=.TRUE.) Canonicalization within the core, virtual, and any rotationally invariant active subspaces yields a well defined theoretical model. You would not normally turn this option off. KROT flag for treating (ij)->(ab) excitations .TRUE. means treating this type of term by the traditional MCQDPT formulae .FALSE. uses a MP2-type formula when this type of term arises between two identical determinants, while using zero otherwise. This is thought to be better in terms of size-consistency. (default) KROT has an impact on run times and on the numerical result. See the paper cited below by Ebisuzaki, Watanabe, and Nakano for details. THRWGT threshold weight on the square of CI coefficients, for determinant selection. Any determinants that are excluded from the reference list due to THRWGT are treated in the outer space of the perturbation. Give as a negative number to retain all of the determinants, even those of very little importance, in the reference of the perturbation treatment. The default is 1.0d-8. KSZDOE flag to use spin (Sz) dependent orbital energies. This variable is ignored for singlet state(s), or if SZ is chosen as 0. If .TRUE., alpha and beta orbital energies are not the same, Ealp(i) = h(i,i) + sum_kl { Dalp(k,l)[(ii|kl)-(il|ki)] +Dbet(k,l) (ii|kl)} Ebet(i) = h(i,i) + sum_kl { Dbet(k,l)[(ii|kl)-(il|ki)] +Dalp(k,l) (ii|kl)} If .FALSE. both sets use the energies E(i) = h(i,i) + sum_kl D(k,l)[(ii|kl)-1/2*(il|ki)] = [Ealp(i)+Ebet(i)]/2 from the total density D(k,l)=Dalp(k,l)+Dbet(k,l) Default=.TRUE. THRGEN threshold on generator constants. Default=1.0d-9 Raising lowers accuracy but produces speedups. Lowering to 1.0d-12 should give full accuracy for benchmarking purposes. THRHDE threshold to ignore |/dE|, which is not a very effective screening, and its use is thus not recommended. Default is 1.0 which should not screen anything. Possible values are 0.05-0.10, since many |/dE| are around 0.02-0.03. The next two deal with the so-called "intruder state avoidance". There are theoretical difficulties with either one. THRDE just drops terms, so the potential surface may have small discontinuities. EDSHFT always shifts results a little bit, even if no small denominators (aka intruder states) are actually present. Clearly both are "band- aids"! Note that the first ISA technique is turned on, by default. THRDE is a threshold to simply drop out any term whose energy denominator is too small. The default for this is 0.005 Hartree. Change to zero to turn this option off. EDSHFT is the same as the same keyword in $MCQDPT. The denominators D are changed to D + EDSHFT/D. Turn off THRDE if you select this option. A reasonable value to try is 0.02, the default is 0.0. 5. miscellaneous data CEXCEN = string defining the units for the excitation energy. Choose from these 4 strings (any case): eV (default), cm-1, Kcal/mol, KJ/mol DDTFPT = a flag requesting the distributed data integral transformation be used, if the run is parallel. This option requires MEMDDI in $SYSTEM. If there is not enough memory to allow this, turn this option off to use an alternate parallel transformation (DEFAULT=.TRUE.). Note: There are additional technical parameters for $GMCPT, documented only in the source code file gmcpt.src. ---- In case it is desirable for the GMC-QDPT program to reproduce results obtained by the DETMRPT/MCQDPT programs: a) use a CAS-SCF reference in the MCSCF step b) select REFTYP=ORMAS here, and enter NSPACE=1, giving only one value for MSTART, MINE, MAXE c) retain the entire CAS reference in the internal determinant's perturbation space, THRWGT=-1.0 d) select the original external determinant space's perturbation treatment, KROT=.FALSE. e) use equal alpha/beta orbital energies, KSZDOE=.FALSE. f) in multi-state mode, select KXGMC off, to reproduce those program's 0-th order reference states g) ensure ISA is turned off, THRDE= -1.0 h) perhaps adjust numerical parameters to full accuracy, to increase the no. of decimals: THRGEN=1D-12, THRHDE=1D+10. References for GMC-QDPT: a) H.Nakano, R.Uchiyama, K.Hirao J.Comput.Chem. 23, 1166-1175(2002) b) M.Miyajima, Y.Watanabe, H.Nakano J.Chem.Phys. 124, 044101/1-9(2006) c) R.Ebisuzaki, Y.Watanabe, H.Nakano Chem.Phys.Lett. 442, 164-169(2007) The first paper introduced the theory, with further developments including reference state weights given in the second. The present computer code is based on the efficient formulation involving ionized intermediate determinants, as described in the third paper. ========================================================== ==========================================================

generated on 7/7/2017