RI_METRIC

This subsection allows for the definition of an exchange RI metric that is different from the main exchange potential. By default (i.e. if this subsection is ignored), the exchange kernel is computed in the V approximation: (ab|ij) = (ab|P) V^-1 (Q|ij), where V = (P|Q). With a RI metric, we have a 2 step RI involving the metric potential for the 3-center integrals: (ab|ij) = (ab!P) (P!Q)^-1 (Q|R) (R!S)^-1 (S!ij), where | stands for the exchange potential and ! for the metric potential. This allows for drastic screening of the 3-center integrals by selecting shorter range metric. [Edit on GitHub]

Keywords

• SECTION_PARAMETERS

• CUTOFF_RADIUS

• OMEGA

• POTENTIAL_TYPE

• T_C_G_DATA

Keyword descriptions

SECTION_PARAMETERS: logical = F

Lone keyword: T

Usage: &EXACT_EXCHANGE {logical}

Enables the use of a RI metric. [Edit on GitHub]

CUTOFF_RADIUS: real = 0.00000000E+000

Aliases: R_C ,RC ,RANGE

Usage: CUTOFF_RADIUS {double}

The cutoff radius (in Angstrom) for the truncated Coulomb operator. [Edit on GitHub]

OMEGA: real = 0.00000000E+000

Usage: OMEGA {double}

The range parameter for the short range operator (in 1/a0). [Edit on GitHub]

POTENTIAL_TYPE: enum = OVERLAP

Aliases: OP ,OPERATOR ,POTENTIAL

Usage: OPERATOR {string}

Valid values:

• OVERLAP Overlap operator (=identity)

• TRUNCATED Truncated Coulomb operator: 1/r if r < R_c, 0 otherwise

• SHORTRANGE Short range: erfc(omega*r)/r

The type of operator used for the metric. [Edit on GitHub]

T_C_G_DATA: string = t_c_g.dat

Usage: T_C_G_DATA {string}

Location of the file t_c_g.dat that contains the data for the evaluation of the truncated gamma function [Edit on GitHub]