$DFTB group (relevant for GBASIS=DFTB) Density-functional tight-binding (DFTB) is turned on by selecting GBASIS=DFTB in $BASIS. $DFTB controls optional parameters for a DFTB calculation. DFTB is formulated in a two-center approximation utilizing implicitly a minimal pseudoatomic orbital basis set with corresponding, pretabulated one- and two-center integrals. Because of this, many properties (for instances, multipoles higher than dipoles) and many options are ignored or not available in the current implementations of DFTB. DFTB also uses an independent SCF driver (SCF in DFTB is also called SCC, see below), so most SCF options are not available for DFTB. Only SCFTYP=RHF and UHF are implemented. SCFTYP=ROHF is available, only when all SPNCST values are zero. DFTB does not explicitly use symmetry (C1 throughout) since integrals are never computed during the calculations. Slater-Koster tables are only defined for spherical functions (5d) so DFTB sets ISPHER=1. Most $GUESS options do not work for DFTB (DFTB does not use initial orbitals in the usual sense). Other than the default (METHOD=HUCKEL, which is ignored), only METHOD=MOREAD works (note that SCC-DFTB can use initial charges on atoms, derived from the orbitals). RUNTYP=OPTIMIZE, HESSIAN and RAMAN are available for full (non-FMO) DFTB, whereas RUNTYP=OPTIMIZE and OPTFMO are available for FMO-DFTB. Excited state calculations for full DFTB may be performed through the standard (linear- response) time-dependent formalism (only closed shell). PCM can be used for both ground and excited state calculations, and energy and gradient can be evaluated. In DFTB calculation, the atom type is determined by its name, not its nuclear charge as elsewhere in GAMESS. The nuclear charge (the second column in $DATA) is used only in population analysis, but not in SCF. DFTB uses a notion of "species", which means an atomic type. The species are numbered according to the order in which atoms appear in $DATA. For instances, in water there are two species, O and H. An atomic type of each species needs MAXANG, which for most but not all atoms is set automatically. NDFTB order of the Taylor expansion of the total energy around a reference density in the DFTB model. = 1 NCC-DFTB, also called DFTB1. NCC stands for non-charge-consistent, i.e., no explicity charge-charge interaction term is included in the energy calculation. = 2 SCC-DFTB, also called DFTB2. SCC means a self-charge-consistent approach, and SCC implies that SCF iterations are carried out that converge monopolar charges towards self-consistency. = 3 DFTB3, including 3rd order correction using Hubbard derivatives (HUBDER). In order to reproduce the published DFTB3 approach, it is necessary to also specify DAMPXH=.TRUE. to add other terms. Gaus, M. et al. J. Chem. Theory Comput. 2011, 7, 931-948 is referred to as Gaus2011 below. Default: 2. DAMPXH = a flag to include the damping function for X-H atomic pair in DFTB3. See also DAMPEX, and eq 21 in Gaus2011. The damping function is used when at least one atom in a pair is "H". "HYDROGEN" and any other name will turn off the damping. Default: .FALSE. DAMPEX = an exponent used in the damping function for X-H atomic pairs. The default value is 4.2 (see Table 2 in Gaus2011 for more details). SRSCC = a flag to perform shell-resolved SCC calculation. If set to .FALSE., the code uses the Hubbard value for an s orbital for p and d orbitals, ignoring their Hubbard values defined in Slater- Koster tables. Using .TRUE. enables the use of proper Hubbard values for p and d orbitals, implemented only for DFTB1 and DFTB2. Default: .FALSE. ITYPMX Convergence method of SCC calculations. = -1 Use standard GAMESS convergence methods. SOSCF and DIIS are supported, but DEM is not. = 0 Broyden's method. Interpolation is applied for atomic (or shell-resolved when SRSCC=.TRUE.) charges, but not Hamiltonian matrix. = 1 (reserved) = 2 DIIS for charges. Default: 0. ETEMP = electronic temperature in Kelvin. Non-zero values of ETEMP help SCF convergence of nearly-degenerate systems by smearing occupation numbers around the Fermi-level. Only the Fermi-Dirac distribution function is available as a smearing function. The default value is 0 Kelvin, meaning the smearing function is not used. ETEMP is implemented only for SCFTYP=RHF and when FMO is not used. DISP dispersion model for DFTB. = NONE no Dispersion correction. = UFF UFF-type dispersion correction. Parameters for atomic numbers up to 54 are available internally or can be supplied in DISPPR for any atom. Built-in parameters are taken from Rappe et al. J. Am. Chem. Soc. 1992, 114, 10024. = SK The Slater-Kirkwood type dispersion correction omitting the change polarizability depending on the number of bonds. No default values of DISPPR are available. Some are listed in the manual of the DFTB+ program. DISPPR an array of parameters used for dispersion correction, listed in sets for each species. For DISP=UFF, DISPPR(1) and DISPPR(2) define the non-bonded distance (Angs.) and energy (kcal/mol) for the first species, respectively, and so on. For DISP=SK, a set for a species has 3 parameters, the polarizability (Angstrom^3), cutoff length (Angstrom), and atomic charge. Default: see DISP. HUBDER an array of Hubbard derivatives for each species (1 per species) used only for DFTB3 calculations. Default values are set only for C, H, N, O, and P using the final row of Table 2 in Gaus2011 (see the paper for other choices). MAXANG array of maximum angular momentum of each species, which determines the number of basis functions. DFTB uses only valence orbitals and electrons! Most elements have proper default values, but for some atomic types (i.e., species) you need to manually define the values. QREF array of the number of reference electrons of each species. QREF is usually automatically taken from Slater-Koster parameters, so this option is seldom used. SPNCST an array of spin constants used in unrestricted (UHF) DFTB calculation. Provide 6 spin constants, W_{ss}, W_{sp}, W_{pp}, W_{sd}, W_{pd}, & W_{dd}, for each species in a continuous array. Constants for some elements can be found in the manual of the DFTB+ program. MODHSS controls the behavior of the computation of analytic Hessian (bit additive). 1 Do not write integrals on disk. 2 Use a faster algorithm for solving CP-DFTB requiring a lot of memory. 4 Parallelize integral transformation using GDDI. 8 Hessian contributions are calculated one by one. By default, all of these flags are set to true, unless there is not enough memory or for some other reason. * * * The following options are FMO-DFTB specific (Nishimoto, Y. et al. J. Chem. Theory Comput. 2014, 10, 4801-4812.). FMO-DFTB has many limitations and some FMO options are not supported (for instance, AFO, multilayer FMO etc). Only single layer, restricted closed-shell FMO2-DFTB1, 2, and 3 are implemented at present. SRSCC, ETEMP etc are not available. The analytic gradient is available for FMO-DFTB, requiring solving SCZV as in other FMO methods. MODESD = controls the behavior of ES-DIM (electrostatic dimer) approximation (bit additive). 1 Calculate interfragment repulsive energy for ES dimers (almost never used). 2 Add up all ES-DIM energies. This means that individual ES dimer energies are not calculated, but only their total lump sum, computed with the dynamic load balancing. 4 Lump ES-DIM routine with static load balancing. The bits of 2 or 4 are mutually exclusive. Default: 0 (i.e., individual ES dimer energies). MODGAM = controls the calculation of gamma values (interatomic 1/R-like function) in FMO-DFTB2 and FMO-DFTB3 (bit additive). 0 Calculate gamma values on the fly. (default) 1 Calculate once and prestore gamma values in triangular matrix. 2 Calculate once and prestore gamma values in square matrix. 4 With the bits of 1 or 2, the calculation of gamma values is parallelized with GDDI. The bits of 1 or 2 are mutually exclusive. These options are faster but takes more memory. Default: 0 ========================================================== ==========================================================

generated on 7/7/2017