ensemble (TTM)

This page describes the two-temperature-model (TTM) integrators ttm and heat_ttm.

Syntax

ttm

The full command is:

ensemble ttm <ttm_gm> <ttm_gid> <Ce> <rho_e> <kappa_e> <gamma_p> <gamma_s> <v_0> <nx> <ny> <nz> <T_e_init> [{optional_args}]

heat_ttm

The full command is:

ensemble heat_ttm <T> <T_coup> <delta_T> <label_source> <label_sink> <ttm_gm> <ttm_gid> <Ce> <rho_e> <kappa_e> <gamma_p> <gamma_s> <v_0> <nx> <ny> <nz> <T_e_init> [{optional_args}]

For heat_ttm, the first five parameters, <T>, <T_coup>, <delta_T>, <label_source>, and <label_sink>, have the same meanings as in heat_lan.

Required parameters

For both ttm and heat_ttm:

  • <ttm_gm> and <ttm_gid> specify the atom group coupled to the electron grid.

  • <Ce> is the electron specific heat per electron.

  • <rho_e> is the electron number density.

  • <kappa_e> is the electron thermal conductivity in eV/(ps K Å).

  • <gamma_p> and <gamma_s> are friction coefficients in amu/ps.

  • <v_0> is the threshold velocity in Å/ps.

  • <nx>, <ny>, and <nz> are the numbers of electron grid cells in the three directions.

  • <T_e_init> is the initial electron temperature in K.

The product <Ce> times is the volumetric electron heat capacity.

Optional arguments

ttm_out_interval

Syntax:

ttm_out_interval <interval>

Set the output interval for ttm_electron_temperature.out. The default value is 1.

ttm_infile

Syntax:

ttm_infile <filename>

Read the initial electron temperature from a file. The file must contain one line for each cell in the form:

ix iy iz T_e

The grid indices are 1-based.

ttm_properties_file

Syntax:

ttm_properties_file <filename>

Read per-cell electron properties from a file. The file must contain one line for each cell in the form:

ix iy iz C_vol kappa_e gamma_p eta

Here, C_vol is the volumetric electron heat capacity, kappa_e is in eV/(ps K Å), gamma_p is in amu/ps, and eta is the source absorption efficiency. This file must define all grid cells and overrides the uniform <Ce>, <rho_e>, <kappa_e>, and <gamma_p> values.

ttm_source

Syntax:

ttm_source <source>

Add a volumetric heat source to the electron grid. The source strength is in eV/(ps Å\(^3\)). When ttm_properties_file is used, the source in each cell is multiplied by eta.

ttm_active_x, ttm_active_y, ttm_active_z

Syntax:

ttm_active_x <range>
ttm_active_y <range>
ttm_active_z <range>

Set the active range of the electron grid in each direction. The range can be all, a single 1-based cell index, or an inclusive interval such as 3:10 or 3-10. Cells outside the active region have zero electron temperature and do not exchange energy with neighboring cells or atoms.

Notes

  • The simulation box for the electron grid is the full MD box.

  • The electron grid is always uniform in real space.

  • Electron-temperature snapshots are written to ttm_electron_temperature.out.

  • In heat_ttm, the source and sink labels always refer to grouping method 0.

Examples

Uniform pure TTM:

ensemble ttm 0 0 1.0 1.0 0.005 0.01 0.0 100.0 1 1 12 300

Pure TTM with an input electron-temperature profile and periodic snapshots:

ensemble ttm 0 0 1.0 1.0 0.005 0.01 0.0 100.0 1 1 12 300 ttm_infile te_init.dat ttm_out_interval 50

Pure TTM with per-cell properties:

ensemble ttm 0 0 1.0 1.0 0.005 0.01 0.0 100.0 1 1 40 300 ttm_properties_file properties.dat ttm_active_z 6:35 ttm_out_interval 100

Heat source/sink plus TTM:

ensemble heat_ttm 300 100 30 0 1 1 0 1.0 1.0 0.005 0.02 0.0 100.0 1 1 40 300 ttm_out_interval 100