# CPHF

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

## Keywords

- ENERGY_GAP

- EPS_CONV

- MAX_ITER

- PRECONDITIONER

## Keyword descriptions

ENERGY_GAP: real = 2.00000000E-001

  Usage: ENERGY_GAP 0.1

  Energy gap estimate [a.u.] for preconditioning [Edit on GitHub]

EPS_CONV: real = 1.00000000E-006

  Usage: EPS_CONV 1.e-6

  Target accuracy for Z-vector euation solution. [Edit on GitHub]

MAX_ITER: integer = 50

  Usage: MAX_ITER 200

  Maximum number of conjugate gradient iteration to be performed for one optimization. [Edit on GitHub]

PRECONDITIONER: enum = FULL_ALL

  Usage: PRECONDITIONER FULL_ALL

  Valid values:

  - `FULL_ALL` Most effective state selective preconditioner based on diagonalization, requires the ENERGY_GAP parameter to be an underestimate of the HOMO-LUMO gap. This preconditioner is recommended for almost all systems, except very large systems where make_preconditioner would dominate the total computational cost.

  - `FULL_SINGLE_INVERSE` Based on H-eS cholesky inversion, similar to FULL_SINGLE in preconditioning efficiency but cheaper to construct, might be somewhat less robust. Recommended for large systems.

  - `FULL_SINGLE` Based on H-eS diagonalisation, not as good as FULL_ALL, but somewhat cheaper to apply.

  - `FULL_KINETIC` Cholesky inversion of S and T, fast construction, robust, and relatively good, use for very large systems.

  - `FULL_S_INVERSE` Cholesky inversion of S, not as good as FULL_KINETIC, yet equally expensive.

  - `NONE` skip preconditioning

  Type of preconditioner to be used with all minimization schemes. They differ in effectiveness, cost of construction, cost of application. Properly preconditioned minimization can be orders of magnitude faster than doing nothing. [Edit on GitHub]