# XALMO_NEWTON_PCG_SOLVER

Controls an iterative solver of the Newton-Raphson linear equation. [Edit on GitHub]

## Keywords

- EPS_ERROR

- EPS_ERROR_EARLY

- MAX_ITER

- MAX_ITER_EARLY

- MAX_ITER_OUTER_LOOP

- PRECONDITIONER

## Keyword descriptions

EPS_ERROR: real = 1.00000000E-005

  Usage: EPS_ERROR 1.E-6

  Target value of the MAX norm of the error [Edit on GitHub]

EPS_ERROR_EARLY: real = -1.00000000E+000

  Usage: EPS_ERROR_EARLY 1.E-2

  Target value of the MAX norm of the error for truncated SCF (e.g. Langevin-corrected MD). Negative values mean that this keyword is not used. [Edit on GitHub]

MAX_ITER: integer = 20

  Usage: MAX_ITER 100

  Maximum number of iterations [Edit on GitHub]

MAX_ITER_EARLY: integer = -1

  Usage: MAX_ITER_EARLY 5

  Maximum number of iterations for truncated SCF (e.g. Langevin-corrected MD). Negative values mean that this keyword is not used. [Edit on GitHub]

MAX_ITER_OUTER_LOOP: integer = 0

  Usage: MAX_ITER_OUTER_LOOP 10

  Maximum number of iterations in the outer loop. Use the outer loop to update the preconditioner and reset the conjugator. This can speed up convergence significantly. [Edit on GitHub]

PRECONDITIONER: enum = DEFAULT

  Usage: PRECONDITIONER DOMAIN

  Valid values:

  - `NONE` Do not use preconditioner

  - `DEFAULT` Same as DOMAIN preconditioner

  - `DOMAIN` Invert preconditioner domain-by-domain. The main component of the linear scaling algorithm

  - `FULL` Solve linear equations step=-H.grad on the entire space

  Select a preconditioner for the conjugate gradient optimization [Edit on GitHub]