# CPHF

References: DelBen2013

Parameters influencing the solution of the Z-vector equations in MP2 gradients calculations. [Edit on GitHub]

## Keywords

- DO_POLAK_RIBIERE

- ENFORCE_DECREASE

- EPS_CONV

- MAX_ITER

- RECALC_RESIDUAL

- RESTART_EVERY

- SCALE_STEP_SIZE

- SOLVER_METHOD

## Keyword descriptions

DO_POLAK_RIBIERE: logical = F

  Lone keyword: `T`

  Usage: DO_POLAK_RIBIERE T

  Use a Polak-Ribiere update of the search vector in CG instead of the Fletcher Reeves update. Improves the convergence with modified step sizes. Ignored with other methods than CG. [Edit on GitHub]

ENFORCE_DECREASE: logical = F

  Lone keyword: `T`

  Usage: ENFORCE_DECREASE T

  Restarts if residual does not decrease. [Edit on GitHub]

EPS_CONV: real = 1.00000000E-004

  Usage: EPS_CONV 1.0E-6

  Convergence threshold for the solution of the Z-vector equations. The Z-vector equations have the form of a linear system of equations Ax=b, convergence is achieved when |Ax-b|<=EPS_CONV. [Edit on GitHub]

MAX_ITER: integer = 30

  Aliases: MAX_NUM_ITER

  Usage: MAX_ITER 50

  Maximum number of iterations allowed for the solution of the Z-vector equations. [Edit on GitHub]

RECALC_RESIDUAL: logical = F

  Lone keyword: `T`

  Usage: RECALC_RESIDUAL T

  Recalculates residual in every step. [Edit on GitHub]

RESTART_EVERY: integer = 5

  Usage: RESTART_EVERY 5

  Restart iteration every given number of steps. [Edit on GitHub]

SCALE_STEP_SIZE: real = 1.00000000E+000

  Usage: SCALE_STEP_SIZE 1.0

  Scaling factor of each step. [Edit on GitHub]

SOLVER_METHOD: enum = POPLE

  Usage: SOLVER_METHOD POPLE

  Valid values:

  - `POPLE` Pople’s method (Default).

  - `CG` Conjugated gradient method (equivalent to Pople).

  - `RICHARDSON` Richardson iteration

  - `SD` Steepest Descent iteration

  Chose solver of the z-vector equations. [Edit on GitHub]