# SHELL

Section can be repeated.

References: Dick1958, Mitchell1993, Devynck2012

This section specifies the parameters for shell-model potentials [Edit on GitHub]

## Keywords

- SECTION_PARAMETERS

- CORE_CHARGE

- K2_SPRING

- K4_SPRING

- MASS_FRACTION

- MAX_DISTANCE

- SHELL_CHARGE

- SHELL_CUTOFF

## Keyword descriptions

SECTION_PARAMETERS: string = DEFAULT

  Usage: H

  The kind for which the shell potential parameters are given [Edit on GitHub]

CORE_CHARGE: real = 0.00000000E+000

  Aliases: CORE

  Usage: CORE_CHARGE {real}

  Partial charge assigned to the core (electron charge units) [Edit on GitHub]

K2_SPRING: real = -1.00000000E+000 [bohr^-2*hartree]

  Aliases: K2 ,SPRING

  Usage: K2_SPRING {real}

  Force constant k2 of the spring potential 1/2k2r^2 + 1/24k4r^4 binding a core-shell pair when a core-shell potential is employed. [Edit on GitHub]

K4_SPRING: real = 0.00000000E+000 [bohr^-4*hartree]

  Aliases: K4

  Usage: K4_SPRING {real}

  Force constant k4 of the spring potential 1/2k2r^2 + 1/24k4r^4 binding a core-shell pair when a core-shell potential is employed. By default a harmonic spring potential is used, i.e. k4 is zero. [Edit on GitHub]

MASS_FRACTION: real = 1.00000000E-001

  Aliases: MASS

  Usage: MASS_FRACTION {real}

  Fraction of the mass of the atom to be assigned to the shell [Edit on GitHub]

MAX_DISTANCE: real = -5.29177209E-001 [angstrom]

  Usage: MAX_DISTANCE 0.0

  Assign a maximum elongation of the spring, if negative no limit is imposed [Edit on GitHub]

SHELL_CHARGE: real = 0.00000000E+000

  Aliases: SHELL

  Usage: SHELL_CHARGE {real}

  Partial charge assigned to the shell (electron charge units) [Edit on GitHub]

SHELL_CUTOFF: real = -5.29177209E-001 [angstrom]

  Usage: SHELL_CUTOFF -1.0

  Define a screening function to exclude some neighbors of the shell when electrostatic interaction are considered, if negative no screening is operated [Edit on GitHub]