# RI_METRIC

Sets up RI metric [Edit on GitHub]

## Keywords

- CUTOFF_RADIUS

- EPS_RANGE

- OMEGA

- POTENTIAL_TYPE

- T_C_G_DATA

## Keyword descriptions

CUTOFF_RADIUS: real = 3.00000000E+000 [angstrom]

  Usage: CUTOFF_RADIUS 3.0

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

EPS_RANGE: real = 1.00000000E-008

  The threshold to determine the effective range of the short range RI metric: erfc(omega*eff_range)/eff_range = EPS_RANGE [Edit on GitHub]

OMEGA: real = 0.00000000E+000

  Usage: OMEGA 0.5

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

POTENTIAL_TYPE: enum = DEFAULT

  Usage: POTENTIAL_TYPE DEFAULT

  Valid values:

  - `DEFAULT` Use Coulomb metric for RI-MP2 and normal-scaling RI-SOS-MP2, RI-RPA and GW. Use Overlap metric for low-scaling RI-SOS-MP2, RI-RPA and GW for periodic systems. Use truncated Coulomb metric for low-scaling RI-SOS-MP2, RI-RPA and GW for non-periodic systems.

  - `COULOMB` Coulomb metric: 1/r. Recommended for RI-MP2,

  - `IDENTITY` Overlap metric: delta(r).

  - `LONGRANGE` Longrange metric: erf(omega*r)/r. Not recommended with DO_SVD .TRUE.

  - `SHORTRANGE` Shortrange metric: erfc(omega*r)/r

  - `TRUNCATED` Truncated Coulomb metric: if (r < R_c) 1/r else 0. More accurate than IDENTITY for non-periodic systems. Recommended for low-scaling methods.

  Decides which operator/metric is used for resolution of the identity (RI). [Edit on GitHub]

T_C_G_DATA: string = t_c_g.dat

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