Section 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.

• Section path: CP2K_INPUT / FORCE_EVAL / DFT / XAS_TDP / KERNEL / EXACT_EXCHANGE / RI_METRIC

• This section cannot be repeated.

• Subsections

  • none

• Keywords

  • SECTION_PARAMETERS
  • CUTOFF_RADIUS
  • OMEGA
  • POTENTIAL_TYPE
  • T_C_G_DATA

• Keyword descriptions

  SECTION_PARAMETERS
  	&RI_METRIC {Logical}
  	Enables the use of a RI metric.
  	This keyword cannot be repeated and it expects precisely one logical.
  	The lone keyword behaves as a switch to .TRUE.
  	Default value: .FALSE.

  CUTOFF_RADIUS
  	CUTOFF_RADIUS {Real}
  	The cutoff radius (in Angstrom) for the truncated Coulomb operator.
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 0.00000000E+000
  	Alias names for this keyword: R_C, RC, RANGE

  OMEGA
  	OMEGA {Real}
  	The range parameter for the short range operator (in 1/a0).
  	This keyword cannot be repeated and it expects precisely one real.
  	Default value: 0.00000000E+000

  POTENTIAL_TYPE
  	POTENTIAL_TYPE {Keyword}
  	The type of operator used for the metric.
  	This keyword cannot be repeated and it expects precisely one keyword.
  	Default value: OVERLAP
  	List of valid keywords: OVERLAP Overlap operator (=identity) SHORTRANGE Short range: erfc(omega*r)/r TRUNCATED Truncated Coulomb operator: 1/r if r < R_c, 0 otherwise
  	Alias names for this keyword: OP, OPERATOR, POTENTIAL

  T_C_G_DATA
  	T_C_G_DATA {Word}
  	Location of the file t_c_g.dat that contains the data for the evaluation of the truncated gamma function
  	This keyword cannot be repeated and it expects precisely one word.
  	Default value: t_c_g.dat