# OPT_RI_BASIS

References: DelBen2013

Parameters influencing the optimization of the RI MP2 basis. Only exponents of non-contracted auxiliary basis can be optimized. An initial RI auxiliary basis has to be specified. [Edit on GitHub]

## Keywords

- SECTION_PARAMETERS

- BASIS_SIZE

- DELTA_I_REL

- DELTA_RI

- EPS_DERIV

- MAX_ITER

- NUM_FUNC

## Keyword descriptions

SECTION_PARAMETERS: logical = F

  Lone keyword: `T`

  Usage: &OPT_RI_BASIS .TRUE.

  Putting the &OPT_RI_BASIS section activates optimization of RI basis. [Edit on GitHub]

BASIS_SIZE: enum = MEDIUM

  Usage: BASIS_SIZE (MEDIUM|LARGE|VERY_LARGE)

  Valid values:

  - `MEDIUM`

  - `LARGE`

  - `VERY_LARGE`

  Specifies the size of the auxiliary basis set automatically generated as initial guess. This will be effective only if RI_AUX_BASIS_SET in the KIND section and NUM_FUNC are not specified. [Edit on GitHub]

DELTA_I_REL: real = 1.00000000E-006

  Aliases: DI_REL

  Usage: DELTA_I_REL 1.0E-6_dp

  Target accuracy in the relative deviation of the amplitudes calculated with and without RI approximation, (more details in Chem.Phys.Lett.294(1998)143). [Edit on GitHub]

DELTA_RI: real = 5.00000000E-006

  Aliases: DRI

  Usage: DELTA_RI 1.0E-6_dp

  Target accuracy in the absolute difference between the RI-MP2 and the exact MP2 energy, DRI=ABS(E_MP2-E_RI-MP2). [Edit on GitHub]

EPS_DERIV: real = 1.00000000E-003

  Aliases: EPS_NUM_DERIV

  Usage: EPS_DERIV 1.0E-3_dp

  The derivatives of the MP2 energy with respect to the exponents of the basis are calculated numerically. The change in the exponent a_i employed for the numerical evaluation is defined as h_i=EPS_DERIV*a_i. [Edit on GitHub]

MAX_ITER: integer = 50

  Aliases: MAX_NUM_ITER

  Usage: MAX_ITER 100

  Specifies the maximum number of steps in the RI basis optimization. [Edit on GitHub]

NUM_FUNC: integer[ ] = -1

  Usage: NUM_FUNC {number of s func.} {number of p func.} …

  Specifies the number of function, for each angular momentum (s, p, d …), employed in the automatically generated initial guess. This will be effective only if RI_AUX_BASIS_SET in the KIND section is not specified. [Edit on GitHub]