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17 THE DENSITY FUNCTIONAL PROGRAM

Density-functional theory calculations may be performed using one of the following commands:
DFT
calculate functional of a previously computed density.
RKS or RKS-SCF
calls the spin-restricted Kohn-Sham program. KS and KS-SCF are aliases for RKS.
UKS or UKS-SCF
calls the spin-unrestricted Kohn-Sham program
Each of these commands may be qualified with the key-names of the functional(s) which are to be used, and further options:

command, key1, key2, key3, $\ldots$, options

If no functional keyname is given,the default is LDA (see below). Following this command may appear directives specifying options for the density-functional modules (see section 17.2) or the Hartree-Fock program (see section 16.1).

On completion of the functional evaluation, or self-consistent Kohn-Sham calculation, the values of the individual functionals are stored in the MOLPRO vector variable DFTFUNS; the total is in DFTFUN, and the corresponding individual functional names in DFTNAME.

Energy gradients are available for self-consistent Kohn-Sham calculations.

Density fitting can be used for closed and open-shell spin-restricted KF and is involked by a prefix DF- (DF-KS or DF-RKS, see section 15). For UKS, only Coulomb fitting is possible (CF-UKS). Density fitting is highly recommended (unless explicit symmetry handling is required), as the induced errors are negligible and it offers massive speed increases, particularly for pure functionals. For details see R. Polly, H.-J. Werner, F. R. Manby, and Peter J. Knowles, Fast Hartree-Fock theory using local density fitting approximations, Mol. Phys. 102, 2311 (2004). All publications resulting from DF-HF or DF-KS calculations should cite this work.

Normally, sensible defaults are used to define the integration grid. The accuracy can be controlled using options as described in section 17.1 or directives as described in section 17.2). More control is provided by the GRID command, as described in section 17.3.



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