*FDE¶

Frozen density embedding (FDE) directives.

General information on the FDE method can be found in recent reviews (e.g. [Jacob2013], [Gomes2012a]), whereas details concerning the Dirac implementation are found in [Gomes2008], [Hofener2012] and [Hofener2013].

Data import¶

If Dirac is used to calculate the subsystem of interest, data from the subsystem(s) making up the environment must be fed into the program.

.EMBPOT¶

Specifies the name of the file containing the embedding potential over an integration grid.

Default:

.EMBPOT
EMBPOT

.FRDENS¶

Specifies the name of the file containing the “frozen” quantities (integration grid, electrostatic potential, electrostatic potential due to external fields (e.g. point charges), density and (x,y,z) components of the density gradient).

Default:

.FRDENS
FRZDNS

Embedding potential¶

If the .EMBPOT option was selected, the program will simple compute matrix elements of the the AO basis used by the program, and add it to the one-electron Fock matrix. Because of that, this option can be used with any wavefunction in Dirac. The ground-state calculation in this case corresponds to the “fixed potential” scheme of [Gomes2008].

However, if .EMBPOT is not specified, the program implicitly selects the .UPDATE option, and assumes a frozen density has been provided (see .FRDENS).

.UPDATE¶

This option requires that the embedding potential for the ground-state be calculated using the “frozen” quantities and those for the subsystem treated with Dirac. The non-additive contributions are calculted with the orbital-free kinetic energy and exchange-correlation density functionals specified under .NAKEF and .NAXCF, respectively.

Currently this option is only supported during the SCF procedure, so it does not have any effect for correlated wavefunctions (e.g. MP2, CI, CC).

The .EMBPOT and this option cannot be specified at the same time.

.NAKEF¶

Specifies the orbital-free kinetic energy density functional used to calculate the non-additive kinetic energy contributions to the ground-state embedding potential (see .UPDATE) and/or response contributions (see .RSP or .RSPLDA)

Default:

.NAKEF
kin_tf

Which corresponds to the Thomas-Fermi kinetic energy functional. Other available functionals are: PW91k (kin_pw91).

.NAXCF¶

Specifies the exchange-correlation density functional used to calculate the non-additive kinetic energy contributions to the ground-state embedding potential (see .UPDATE) and/or response contributions (see .RSP or .RSPLDA)

Default:

.NAXCF
lda

Where lda is equivalent to specifying “slaterx=1.0 vwnc=1.0” (without quotes). Other available functionals are: pbe (equivalent to “pbex=1.0 pbec=1.0”), blyp (equivalent to “beckex=1.0 lypc=1.0”), pp86 (equivalent to “pw86x=1.0 p86c=1.0”)

Response contributions¶

For response-based approaches (TDHF, TDDFT), contributions from FDE to the active subsystem can be included through the keywords below (the default is to not include any). For correlated wavefunctions (e.g. MP2, CI, CC) these do not yet have any effect.

These options can be used together with either .UPDATE or .EMBPOT, but require that “frozen” quantities are present (see .FRDENS)

.RSP¶

Specifies that FDE response contributions should be calculated employing the density functionals specified under .NAKEF and .NAXCF, if any.

.RSPLDA¶

Specifies that the non-additive exchange-correlation and kinetic energy FDE response contributions should be calculated with the LDA and Thomas-Fermi functionals, respectively.

Data export¶

Dirac can also provide ground-state data (density and density gradient, electrostatic potential etc) from the subsystem in question over a grid, so that these can be used by other programs.

.GRIDOU¶

Warning

Development version only.

Specifies the grid over which the quantities will be calculated and exported, and enables the export. The input is a XYZW file, and the output is in XML format. The original file is overwritten.

Default:

.GRIDOU
GRIDOUT

.LEVEL¶

Warning

Development version only.

Specifies which kind of wavefunction will be used to obtain the exported quantities

Default:

.LEVEL
DHF

which corresponds to SCF (Hartree-Fock, DFT) ones. Also supported: MP2.

.EXONLY¶

Warning

Development version only.

This option forces the program to skip the calculation of any FDE contributions, and proceed to exporting the

Debug/expert options¶

.SKIPX¶

Specifies that the non-additive exchange-correlation contributions are not to be calculated.

.SKIPK¶

Specifies that the non-additive kinetic energy contributions are not to be calculated.