$MCQDPT group (relevant if SCFTYP=MCSCF and MPLEVL=2) Controls 2nd order MCQDPT (multiconfiguration quasi- degenerate perturbation theory) runs, if requested by MPLEVL=2 in $CONTRL. MCQDPT2 is implemented only for FORS (aka CASSCF) wavefunctions. The MCQDPT method is a multistate, as well as multireference perturbation theory. The implementation is a separate program, interfaced to GAMESS, with its own procedures for determination of the canonical MOs, CSF generation, integral transformation, CI in the reference CAS, etc. Therefore some of the input in this group repeats data given elsewhere, particularly for $DET/$DRT. Analytic gradients are not available. Spin-orbit coupling may be treated as a perturbation, included at the same time as the energy perturbation. If spin-orbit calculations are performed, the input groups for each multiplicity are named $MCQD1, $MCQD2, ... rather than $MCQDPT. Parallel calculation is enabled. When applied to only one state, the theory is known as multi-reference Moller-Plesset (MRMP), but the term MCQDPT is used when this theory is used in its multi-state form. Please note that this perturbation theory is not the same thing as the CASPT2 theory, and should -NEVER- be called that. A more complete discussion may be found in the 'Further Information' chapter. Most values will inherit sensible defaults for the state symmetry and the orbital space counts from the $DET or $DRT input defining the MCSCF: however for multi-state runs, the user probably has to supply the desired state and weighting information. In case of diabatic state generation at the MCQDPT level, the settings for state selection and weights will be inherited from the $DIABAT input, to be the same as used for the Diabatic MO generation. Thus diabatization runs will probably not give any input here, although they might override NMOFZC/NMODOC defaults. *** MCSCF reference wavefunction *** NEL = total number of electrons, including core. (default from $DATA and ICHARG in $CONTRL) MULT = spin multiplicity (default from $CONTRL) NMOACT = Number of orbitals in FORS active space (default is the active space in $DET or $DRT) NMOFZC = number of frozen core orbitals, NOT correlated in the perturbation calculation. (default is number of chemical cores) NMODOC = number of orbitals which are doubly occupied in every MCSCF configuration, that is, not active orbitals, which are to be included in the perturbation calculation. (The default is all valence orbitals between the chemical core and the active space) NMOFZV = number of frozen virtuals, NOT occupied during the perturbation calculation. The default is to use all virtuals in the MP2. (default=0) If the input file does not provide a $DET or $DRT, the user must give NMOFZC, NMODOC, and NMOACT correctly here. STSYM = The symmetry of the target electronic state(s). See $DET for possible values: use AP/APP in Cs, not primes. This must be given, and need not match the state symmetry used in optimizing the orbitals by $DET or $DRT, although it often does. Default is the totally symmetric representation. NOSYM = 0 use CSF symmetry (see the STSYM keyword). off diagonal perturbations vanish if states are of different symmetry, so the most efficient computation is a separate run for every space symmetry. (default) 1 turn off CSF state symmetry so that all states are treated at once. STSYM is ignored. Presently this option does not seem to work!! -1 Symmetry purify the orbitals. Since $GUESS is not read by MCQDPT runs, this option can be used as a substitute for its PURIFY. After cleaning the orbitals, they are reorthogonalised within each irrep and within each group (core, double, active, virtual) separately. Since this occurs without MCSCF optimization if you have chosen to use RDVECS in $MRMP, it is *your* responsibility to ensure that any purification of the orbitals is small enough that the CAS energies for the original CASSCF and the CAS-CI performed during the MCQDPT are the same! *** perturbation specification *** KSTATE= state is used (1) or not (0) in the MCQDPT2. Maximum of 20 elements, including zeros. For example, if you want the perturbation correction to the second and the fourth roots, KSTATE(1)=0,1,0,1 See also WSTATE. (normal default=1,0,0,0,0,0,0,...) (default for DIABAT=.TRUE. will be from $DIABAT) XZERO a flag to choose the 0-th order Hamiltonian used, when more than one state is included by KSTATE and WSTATE. XZERO 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 .FALSE. *** Intruder State Removal *** EDSHFT = energy denominator shifts. (default=0.0,0.0) See also REFWGT. Intruder State Avoidance (ISA) calculations can be made by changing the energy denominators around poles (where the denominator is zero). Each denominator x is replaced by x + EDSHFT/x, so that far from the poles (when x is large) the effect of such change is small. EDSHFT is an array of two values, the first is used in spin-free MCQDPT, and the second is for spin-orbit MCQDPT. Both values are used if RUNTYP=TRNSTN, only the first is used otherwise. A suggested pair of values is 0.02,0.1, but experimentation with your system is recommended. Setting these values to zero is ordinary MCQDPT, whereas infinite collapses to the MCSCF reference. Note that the energy denominators (which are ket-dependent in MCQDPT) are changed in a different way for each ket- vector, that is, for each row in MCQDPT Hamiltonian matrix. In other words, the zeroth order energies are not "universal", but state specific. This is strictly speaking an inconsistency in defining zeroth order energies that are usually chosen "universally". In order to maintain continuity when studying a PES, one usually uses the same EDSHFT values for all points on PES. In order to study the potential surface for any extended range of geometries, it is recommended to use ISA, as it is quite likely that one or more regions of the PES will be unphysical due to intruder states. For an example of how intruder states can appear at some points on the PES, see Figures 1,2,7 of K.R.Glaesemann, M.S.Gordon, H.Nakano Phys.Chem.Chem.Phys. 1, 967-975(1999) and also H.A.Witek, D.G.Fedorov, K.Hirao, A.Viel, P.-O.Widmark J.Chem.Phys. 116, 8396-406(2002) For a discussion of intruder state removal from MCQDPT, see H.A.Witek, Y.-K.Choe, J.P.Finley, K.Hirao J.Comput.Chem. 23, 957-965(2002) REFWGT = a flag to request decomposition of the second order energy into internal, semi-internal, and external contributions, and to obtain the weight of the MCSCF reference in the 1st order wave function. This option significantly increases the run time! When you run in parallel, only the transformation steps will speed up, as the PT part of the reference weight calculation has not been adapted for speedups (default=.FALSE.) The EDSHFT option does not apply if REFWGT is used. One purpose of using REFWGT is to try to understand the nature of the intruder states. *** Canonical Fock orbitals *** IFORB = 0 skip canonicalization (default when DIABAT=.TRUE.). = 1 determine the canonical Fock orbitals. (the usual default) = 3 canonicalise the Fock orbitals averaged over all $MCQDx input groups. IFORB=3 option pertains only to RUNTYP=TRANSITN. It is primarily meant to include spin-orbit coupling perturbation into the energy perturbation, but could also be used in conjunction with OPERAT=DM to calculate only the second order energy perturbation. IFORB=3 means that WSTATE is used as follows: In each $MCQDx group, the WSTATE weights are divided by the total number of states (sum(i) IROOTS(i)), so the sum over all WSTATE values in all $MCQDx groups is normalized to sum to 1. Thus there is no normalization to 1 within each $MCQDx group. This option might be used to speed up an atomic MCQDPT, e.g. if computing the 3-P ground state of carbon, one would want to average over all three spatial components of the P term, to be sure of spatial degeneracy, but then run the perturbation using symmetry, separately on the B1g+B2g+B3g subspecies (within D2h) of a P term. It is very important to give weights appropriate for the symmetry, the input requires care. WSTATE = weight of each CAS-CI state in computing the closed shell Fock matrix. You must enter 0.0 whenever the same element in KSTATE is 0. In most cases setting the WSTATEs for states to be included in the MCQDPT to equal weights is the best, and this is the default. Runs with DIABAT=.TRUE. default to the same weights used during the DMO generation step. *** Miscellaneous options *** ISELCT is an option to select only the important CSFs for inclusion into the CAS-CI reference states. Set to 1 to select, or 0 to avoid selection of CSFs (default = 0) All CSFs in a preliminary complete active space CI whose CI coefficients exceed the square root of THRWGT are kept in a smaller CI to determine the zero-th order states. Note that the CSFs with smaller coefficients, while excluded from the reference states, are still used during the perturbation calculation, so most of their energy contribution is still retained. This can save appreciable computer time in cases with large active spaces. THRWGT = weight threshold for retaining CSFs in selected configuration runs. In quantum mechanics, the weight of a CSF is the square of its CI coefficient. (default=1d-6) THRGEN = threshold for one-, two-, and three-body density matrix elements in the perturbation calculation. The default gives about 5 decimal place accuracy in energies. Increase to 1.0D-12 if you wish to obtain higher accuracy, for example, in numerical gradients (default=1D-8). Tightening THRGRN and perhaps CI diagonalization should allow 7-8 decimal place agreement with the determinant code. THRENE = threshold for the energy convergence in the Davidson's method CAS-CI. (default=-1.0D+00) THRCON = threshold for the vector convergence in the Davidson's method CAS-CI. (default=1.0D-06) MDI = dimension of small Hamiltonian diagonalized to prepare initial guess CI states. (default=50) MXBASE = maximum number of expansion vectors in the Davidson diagonalization subspace (e.g. MXXPAN). (default=50) NSOLUT = number of states to be solved for in the Davidson's method, this might need to exceed the number of states in the perturbation treatment in order to "capture" the correct roots. NSTOP = maximum number of iterations to permit in the Davidson's diagonalization. LPOUT = print option, 0 gives normal printout, while <0 gives debug print (e.g. -1, -5, -10, -100) In particular, LPOUT=-1 gives more detailed timing information. (default=0) The next three parameters refer to parallel execution: DOORD0 = a flag to select reordering of AO integrals which speeds the integral transformations. This reduces disk writes, but increases disk reads, so you can try turning it off if your machine has slow writes. (default=.TRUE.) PARAIO = access 2e- integral file on every node, at the same time. This affects only runs with DOORD0 true, and it may be useful to turn this off in the case of SMP nodes sharing a common disk drive. (default=.TRUE.) DELSCR = a flag to delete file 56 containing half- transformed integrals after it has been used. This reduces total disk requirements if this file is big. (default=.FALSE.) Note that parallel execution will be more effective if you use distributed memory, MEMDDI in $SYSTEM. Using AOINTS=DIST in $TRANS is likely to be helpful in situations with relatively poor I/O rates compared to communication, e.g. SMP enclosures forced to share a single scratch disk system. See PROG.DOC for more information on parallel execution. Finally, there are additional very specialized options, described in the source code routine MQREAD: IROT, LENGTH, MAXCSF, MAXERI, MAXROW, MXTRFR, THRERI, MAINCS, NSTATE ========================================================== ===========================================================

generated on 7/7/2017