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37.9 DFSAPT: a density-fitting DFT-SAPT program for arbitrary monomer basis sets

DFSAPT is an alternative density-fitting DFT-SAPT program which works with arbitrary monomer basis sets and which can be used for extended dimer systems of about 800 electrons, see Ref.[8].

For a standard DFSAPT calculation using a dimer centered basis set the Molpro input file looks very similar to a corresponding DF-DFT-SAPT claculation, see example h2o_2-dfsapt.com (section 37.9.1). There are, however, two important points to be taken care of:

important #1
Set oldnorm=1 before any call to the DFSAPT program.
important #2
Add numbers to atom labels in the geometry blocks. These have to have a subsequent ordering, see examples 37.9.1-37.9.4.

A corresponding calculation, in which the water monomers are calculated in their own local basis set (monomer centered basis set calculation) is presented in example h2o_2-mc-dfsapt.com (section 37.9.2). Note, however, that very large basis sets are required to converge the individual interaction energy contributions. In order to improve the basis set convergence, additional midbond functions can be added as is exemplified in example h2o_2-mcplus-dfsapt.com (section 37.9.3). Here the def2-TZVP basis functions for the Neon atom were positioned in between the O$\cdots$H hydrogen bridge.

A complete (DCBS) DFSAPT calculation with additional $\delta$(HF) correction and using the PBE0AC(BRJ) xc potential (with automatic asymptotic correction) is shown in section 37.9.4.

Note that in contrast to the DFT-SAPT/DF-DFT-SAPT programs the exchange-dispersion energy is not calculated on the coupled level. Instead, the coupled $E^{(2)}_{exch-disp}$ energies are estimated by scaling the uncoupled ones with a factor which has been obtained from a linear fit to exact results, see Ref.[8].

The following list shows all options which can be used with the DFSAPT program:

E1P
Calculate $E^{(1)}_{pol}$ (default: 1).
E1X
Calculate $E^{(1)}_{exch}$ (default: 1).
E2I
Calculate $E^{(2)}_{ind}$ (default: 0).
E2XI
Calculate $E^{(2)}_{exch-ind}$ (default: 0).
E2D
Calculate $E^{(2)}_{disp}$ (default: 0).
E2XD
Calculate $E^{(2)}_{exch-disp}$ (default: 0).
ALL
Calculate all SAPT contributions (up to 2nd order) (default: 0).
AUXBAS
Auxiliary basis set (default: MP2FIT).
NFREQ
Number of frequencies for computing the monomer response matrices (default: 10).
GRIDTHR
Threshold for grid accuracy (default: 1d-10).
THRKERN
Threshold for density in xc kernel calculation (default: 1d-12).
PRINT
Print flag (default: 0).
W0
Value effects Gauss-Legendre quadrature for computing the response function (see Amos,Handy,Knowles,Rice,Stone,J. Phys.Chem. 89 (1985) 2186) (default: 2d0)
FEXX
Exact exchange factor in response calculations (default: 0d0).
FXC
Exchange-correlation factor in response calculations (default: 0d0).
FCOUL
Coulomb contribution factor in response calculations (default: 1d0).
XFAC
Exchange factor in XC kernel (default: 1d0).
CFAC
Correlation factor in XC kernel (default: 1d0).
AUXMAX
Maximum block size of auxiliary function space for three-index integrals of the type (aux$\vert$orb.orb) (default: 50).
MOMAX
Maximum block size of orbital function space for three-index integrals of the type (orb$\vert$orb.aux) (default: 50).
FXCSING
Singularity correction for XC kernel matrix (default: 0)
THRDUM
Threshold for density calculated at dummy function gridpoints (which can serve as a singularity correction for the calculation of the XC kernel matrix) (default: 1d-4).
COMP
Write 3-index integrals compressed to disk (to save disk space) (default: 0).
THRC
Threshold for 3-index integral calculations (integrals which are smaller than the given threshold are not written to disk) (default: 1d-10).
MINB
Minimal bytelength for integral comression (default: 1).
MODE
Switch for alternative DFSAPT driver which can use integral compression (to be evoked by MODE=2) (default: 1).
FXCFIT
Use density fitting for computation of XC contributions in CPKS calculation (default: 0).
CPKS
Switch for different CPKS solvers (default: 1).
CDIRECT
Use integral direct algorithm for computing the (exact) exchange contributions in CPKS calculations, otherwise intergrals of the type (aux$\vert$vir.vir) are written to disk (default: 0).
MAXIT
Maximum number of iteractions in CPKS (default: 60).
THRCG
Threshold for CG/GMRES solver in CPKS calculations (default: 1d-8).
NSYSOLVE
Switch for BiCG (NSYSOLVE=1) or GMRES (NSYSOLVE=2) solver in CPKS calculations (default: 2).
NSUB
Subspace size in GMRES solver (default: 50).
T678
Switch for 3 different computation modes for $E^{(2)}_{exch-disp}$. T678=3 is recommended for the calculation of large systems but requires more disk space to store intermediate quantities (default: 1).



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