SHELL_OPT

This section sets the environment for the optimization of the shell-core distances that might turn to be necessary along a MD run using a shell-model potential. The optimization procedure is activated when at least one of the shell-core pairs becomes too elongated, i.e. when the assumption of point dipole is not longer valid. [Edit on GitHub]

Subsections

• BFGS
• CG
• LBFGS
• PRINT

Keywords

• EPS_SYMMETRY

• KEEP_SPACE_GROUP

• MAX_DR

• MAX_FORCE

• MAX_ITER

• OPTIMIZER

• RMS_DR

• RMS_FORCE

• SPGR_PRINT_ATOMS

• STEP_START_VAL

• SYMM_EXCLUDE_RANGE

• SYMM_REDUCTION

Keyword descriptions

EPS_SYMMETRY: real = 1.00000000E-004

Usage: EPS_SYMMETRY {REAL}

Accuracy for space group determination. EPS_SYMMETRY is dimensionless. Roughly speaking, two scaled (fractional) atomic positions v1, v2 are considered identical if |v1 - v2| < EPS_SYMMETRY. [Edit on GitHub]

KEEP_SPACE_GROUP: logical = F

Lone keyword: T

Usage: KEEP_SPACE_GROUP .TRUE.

Detect space group of the system and preserve it during optimization. The space group symmetry is applied to coordinates, forces, and the stress tensor. It works for supercell. It does not affect/reduce computational cost. Use EPS_SYMMETRY to adjust the detection threshold. [Edit on GitHub]

MAX_DR: real = 3.00000000E-003 [bohr]

Usage: MAX_DR {real}

Convergence criterion for the maximum geometry change between the current and the last optimizer iteration. [Edit on GitHub]

MAX_FORCE: real = 4.50000000E-004 [bohr^-1*hartree]

Usage: MAX_FORCE {real}

Convergence criterion for the maximum force component of the current configuration. [Edit on GitHub]

MAX_ITER: integer = 200

Usage: MAX_ITER {integer}

Specifies the maximum number of geometry optimization steps. One step might imply several force evaluations for the CG and LBFGS optimizers. [Edit on GitHub]

OPTIMIZER: enum = BFGS

Aliases: MINIMIZER

Usage: OPTIMIZER {BFGS|LBFGS|CG}

Valid values:

• BFGS Most efficient minimizer, but only for ‘small’ systems, as it relies on diagonalization of a full Hessian matrix

• LBFGS Limited-memory variant of BFGS suitable for large systems. Not as well fine-tuned but can be more robust.

• CG conjugate gradients, robust minimizer (depending on the line search) also OK for large systems

References: Byrd1995

Specify which method to use to perform a geometry optimization. [Edit on GitHub]

RMS_DR: real = 1.50000000E-003 [bohr]

Usage: RMS_DR {real}

Convergence criterion for the root mean square (RMS) geometry change between the current and the last optimizer iteration. [Edit on GitHub]

RMS_FORCE: real = 3.00000000E-004 [bohr^-1*hartree]

Usage: RMS_FORCE {real}

Convergence criterion for the root mean square (RMS) force of the current configuration. [Edit on GitHub]

SPGR_PRINT_ATOMS: logical = F

Lone keyword: T

Print equivalent atoms list for each space group symmetry operation. [Edit on GitHub]

STEP_START_VAL: integer = 0

Usage: step_start_val

The starting step value for the SHELL_OPT module. [Edit on GitHub]

SYMM_EXCLUDE_RANGE: integer[2]

Keyword can be repeated.

Usage: SYMM_EXCLUDE_RANGE {Int} {Int}

Range of atoms to exclude from space group symmetry. These atoms are excluded from both identification and enforcement. This keyword can be repeated. [Edit on GitHub]

SYMM_REDUCTION: real[3] = 0.00000000E+000 0.00000000E+000 0.00000000E+000

Usage: SYMM_REDUCTION 0.0 0.0 0.0

Direction of the external static electric field. Some symmetry operations are not compatible with the direction of an electric field. These operations are used when enforcing the space group. [Edit on GitHub]