A modified two temperature molecular dynamics (2T-MD) model for cascades

Modification to the 2T-MD Model for Cutoff in Electronic-Phonon Coupling

These changes are to introduce a reformulation of the traditional 2T-MD scheme to overcome the limitations on the treatment of the high-energy particles by addressing the spurious double-interaction of high-energy atoms with electrons. In this modification we:

Removed the thermalisation time from the start of the cascade by ensuring that we only apply the electronic stopping to the high-energy particles and not electron-phonon coupling (as this is an equilibrium process).
If a particle is subject to electronic stopping we do not include it in the temperature for the ionic voxel, to stop fast-moving particles causing the temperature of a whole voxel to be very high leading to electron-phonon coupling that should not occur.

Changes in the source files:

control.f90:

Line 1327: Retrieve elph_cut and check if it is greater than 0 (Subroutine read_ttm).

Line 3974: Set elph_cut in the table (Subroutine initialise_control).

control_output.F90:

Line 1219: Write elph_cut if the cutoff is activated in the output file (Subroutine write_ttm).

old_control.f90:

Line 2603: Add a condition to evaluate elph_cut and activate the cutoff approach (Subroutine read_control).

Line 4451: Implement an evaluation of elph_cut, read the cutoff parameter, and set elph_cut_sq (Subroutine scan_control).

ttm.f90:

Line 121: Initialise logical variable use_elph_cut.

Line 169: Initialise real variables elph_cut and elph_cut_sq.

ttm_track.f90:

Line 600: Evaluate and include only low-energy ions in the temporary estimate and e-ph coupling if the cutoff is activated (ttm_ion_temperature).
This method is described in the article, DOI: 10.1088/1361-648X/ad4941.

How to use it:

CONTROL:

keyword: ttm_e-phonon_cutoff_velocity
value: float
[unit]: distance/time

Example: ttm_e-phonon_cutoff_velocity 20.0 ang/ps

Old CONTROL format:

keyword: ttm elph_cut
value: float

Example: ttm elph_cut 20.0