The Integral keyword modifies the method of computation and use of two-electron integrals and their derivatives.
Grid=grid
Specifies the integration grid to be used for numerical integrations. Note that it is very important to use the same grid for all calculations where you intend to compare energies (e.g., computing energy differences, heats of formation, and so on).
“Pruned” grids are grids that have been optimized to use the minimal number of points required to achieve a given level of accuracy. Pruned grids are used by default when available (currently defined for H through Kr). For example FineGrid is a pruned (75,302) grid, having 75 radial shells and 302 angular points per shell, resulting in about 7000 points per atom. Grid=UltraFine requests a pruned (99,590) grid. It is recommended for molecules containing lots of tetrahedral centers and for computing very low frequency modes of systems. This grid is also useful for optimizations of larger molecules with many soft modes such as methyl rotations, making such optimizations more reliable.
Other special values for this parameter are CoarseGrid, which requests a pruned version of the (35,110) grid, and SG1Grid, a pruned version of (50,194). Note, however, that the FineGrid has considerably better numerical accuracy and rotational invariance than these other grids, and they are not recommended for production calculations [Krack98]. Pass0Grid requests the obsolete pruned (35,110) grid once intended for pass 0 of a tight SCF calculation.
The default grid is FineGrid. In this case, the default grid for the CPHF is Coarse. When UltraFine is used for the integrals, then SG1 is used for the CPHF; if SG1 is selected as the integration grid, the Coarse grid is again used for the CPHF. When a specific grid is specified to the Integral=Grid option, then that grid is also used for the CPHF. Finally, be aware that SG1 is the default integration grid for a few DFT jobs including Polar=OptRot, Freq=Anharmonic and Freq=NNROA (and Coarse is used in the CPHF in those cases).
The parameter to this option is either a grid name keyword or a specific grid specification. If a keyword is chosen, then the option name itself may be omitted (i.e., Integral(Grid=UltraFineGrid) and Integral(UltraFineGrid) are equivalent).
Specific grids may be selected by giving an integer value N as the argument to Grid. N may have one of these forms:
A large positive integer of the form mmmnnn, which requests a grid with mmm radial shells around each atom, and nnn angular points in each shell. The total number of integration points per atom is thus mmm*nnn. For example, to specify the (99,302) grid, use Int(Grid=99302). The valid numbers of angular points are 38, 50 [Lebedev75], 72 [McLaren63], 86, 110 [Lebedev75], 146, 194, 302 [Lebedev76], 434 [Lebedev80], 590, 770, and 974 [Lebedev92]. If a larger number of angular points is desired, a spherical product grid can be used.
A large negative integer of the form -mmmnnn, which requests mmm radial shells around each atom, and a spherical product grid having nnn θ points and 2*nnn φ points in each shell. The total number of integration points per atom is therefore 2*mmm*nnn2. This form is used to specify the (96,32,64) grid commonly cited in benchmark calculations: Int(Grid=-96032).
DKH
Requests a Douglas-Kroll-Hess 2nd order scalar relativistic calculation [Douglas74, Hess85, Hess86, Jansen89] (see [Barysz01, deJong01] for an overview). This method uses a Gaussian nuclear model [Visscher97]. DKH2 and DouglasKrollHess are synonyms.
NoDKH and NonRelativistic request a non-relativistic core Hamiltonian, which is the default.
DKH0
Requests a Douglas-Kroll-Hess 0th order scalar relativistic calculation.
DKHSO
Requests a Douglas-Kroll-Hess 4th order relativistic calculation including spin-orbit terms (if doing GHF/GKS).
RESC
Requests a RESC scalar relativistic calculation.
SSWeights
Use the weighting scheme of Scuseria and Stratmann [Stratmann96] for the numerical integration for DFT calculations. This is the default.
FMMNAtoms=N
Set the threshold size for turning on FMM by default to N. The default is 60 atoms. Molecules with symmetry have higher crossover points and the threshold is increased accordingly, to 120 atoms for the C2 and Cs point groups and 240 atoms for higher symmetry.
Symm
NoSymm disables and Symm enables the use of symmetry in the evaluation and storage of integrals (Symm is the default). Synonymous with the keywords Symm=[No]Int, which is the recommended usage.
FoFCou
Use routine FoFCou even when it would not otherwise be used. NoFoFCou forbid uses of FoFCou.
LTrace
Trace Linda transactions. Primarily for debugging.
SplitDBFSP
Split density S=P shells into separate S and P shells. NoSplitDBFSP is the default.
ECPAcc=N
Set ECP accuracy parameter to N.
Acc2E=N
Set 2-electron integral accuracy parameter to N.
UnconAOBasis
Uncontract all the primitives in the AO basis. UncontractAOBasis is a synonym for this option.
UnconDBF
Uncontract all the primitives in the density fitting basis. UncontractDensityBasis is a synonym for this option.
NoXCTest
Skip tests of numerical accuracy of XC quadrature.
BasisTransform=N
Transform generalized contraction basis sets to reduce the number of primitives, neglecting primitives with coefficients of 10-N or less. This is the default, with N=4.
ExactBasisTransform
Transform generalized contraction basis sets to reduce the number of primitives, but using only transformations which are exact. Only exact duplicate primitives are removed, and there will be no charge in the energy value.
NoBasisTransform
Do not transform generalized contraction basis sets to reduce the number of primitives.
SCF
Last updated on: 10 May 2009