TheIntegralkeyword 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 thesamegrid 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 exampleFineGridis a pruned (75,302) grid, having 75 radial shells and 302 angular points per shell, resulting in about 7000 points per atom.Grid=UltraFinerequests 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.Grid=SuperFineGridrequests a grid that is about 3x larger thanUltraFineand useful when very high accuracy is desired. The grid specification is (150,974) for the first two rows of the periodic table and (225,974) for later elements.
Other special values for this parameter areCoarseGrid, which requests a pruned version of the (35,110) grid, andSG1Grid, a pruned version of (50,194). Note, however, that theFineGridhas considerably better numerical accuracy and rotational invariance than these other grids, and they arenotrecommended for production calculations[Krack98].Pass0Gridrequests the obsolete pruned (35,110) grid once intended for pass 0 of a tight SCF calculation.
The default grid isFineGrid. In this case, the default grid for the CPHF isCoarse. WhenUltraFineis used for the integrals, thenSG1is used for the CPHF; ifSG1is selected as the integration grid, theCoarsegrid is again used for the CPHF. When a specific grid is specified to theIntegral=Gridoption, then that grid is also used for the CPHF. Finally, be aware thatSG1is the default integration grid for a few DFT jobs includingPolar=OptRot,Freq=AnharmonicandFreq=NNROA(andCoarseis 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)andIntegral(UltraFineGrid)are equivalent).
Specific grids may be selected by giving an integer valueNas the argument to Grid.Nmay have one of these forms:
A large positive integer of the formmmmnnn, which requests a grid withmmmradial shells around each atom, andnnnangular points in each shell. The total number of integration points per atom is thusmmm*nnn. For example, to specify the (99,302) grid, useInt(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 requestsmmmradial shells around each atom, and a spherical product grid havingnnnθ points and 2*nnnφ 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).
Note, that any value fornnnis permitted, although small values are silly (values ofnnn< 15 produce grids of similar size and inferior performance to the special angular grids requested by the second format above). Large values are expensive. For example, a value of 200100 would use 2*200*100*100 or 4 million points per atom!
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].DKH2andDouglasKrollHessare synonyms.
NoDKHandNonRelativisticrequest a non-relativistic core Hamiltonian, which is the default.
DKH0
Requests a Douglas-Kroll-Hess 0thorder 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 toN. 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
NoSymmdisables andSymmenables the use of symmetry in the evaluation and storage of integrals (Symmis the default). Synonymous with the keywordsSymm=[No]Int, which is the recommended usage.
FoFCou
Use routineFoFCoueven when it would not otherwise be used.NoFoFCouforbid uses ofFoFCou.
LTrace
Trace Linda transactions. Primarily for debugging.
SplitDBFSP
Split density S=P shells into separate S and P shells.NoSplitDBFSPis the default.
ECPAcc=N
Set ECP accuracy parameter toN.
Acc2E=N
Set 2-electron integral accuracy parameter toN.
UnconAOBasis
Uncontract all the primitives in the AO basis.UncontractAOBasisis a synonym for this option.
UnconDBF
Uncontract all the primitives in the density fitting basis.UncontractDensityBasisis a synonym for this option.
NoXCTest
Skip tests of numerical accuracy of XC quadrature.
ReadB
Read common/B/from disk after the initial geometry, even if a standard basis was set up.
BasisTransform=N
Transform generalized contraction basis sets to reduce the number of primitives, neglecting primitives with coefficients of 10-Nor less. This is the default, withN=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.
Last update: 7 May 2013