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

Type: logical
Default: F
Lone keyword: T
Usage: &EXACT_EXCHANGE {logical}

Description: Enables the use of a RI metric.

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CUTOFF_RADIUS

Type: real
Default: 0.00000000E+000
Aliases: R_C, RC, RANGE
Usage: CUTOFF_RADIUS {double}

Description: The cutoff radius (in Angstrom) for the truncated Coulomb operator.

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OMEGA

Type: real
Default: 0.00000000E+000
Usage: OMEGA {double}

Description: The range parameter for the short range operator (in 1/a0).

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POTENTIAL_TYPE

Type: enum
Default: OVERLAP
Aliases: OP, OPERATOR, POTENTIAL
Usage: OPERATOR {string}

Description: The type of operator used for the metric.

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

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T_C_G_DATA

Type: string
Default: t_c_g.dat
Usage: T_C_G_DATA {string}

Description: Location of the file t_c_g.dat that contains the data for the evaluation of the truncated gamma function

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