Nonadiabatic processes
nonadiabatic_processes
sets the option to simulate the nonequilibrium phenomena, for example under a radiation cascade, where the electronic stopping and electronicphonon coupling in the later stages of the event will be taken into account according to the eph model [[1]]. MD for the atoms is performed through the use of generalized Langevin dynamics where the random and friction forces are related through the fluctuationdissipation theorem. Here the random and friction forces are given as tensor functions of atomic positions. For the atoms, the force equation that is solved is given as follows:
[math]\displaystyle{ \mathbf{F}_I {{=}} \mathbf{\nabla}_IU_{adiab}  \sum_J B_{IJ}\mathbf{v}_J + \sum_J W_{IJ}\mathbf{\xi}_J }[/math]
The electronic system is considered as a mesh in three dimension and electronic temperature is calculated along with MD by using the finite difference method to solve the nonlinear heat diffusion equation:
[math]\displaystyle{ C_e(T_e)\frac{\partial T_e}{\partial t} = \mathbf{\nabla}.(\kappa_e(T_e)\mathbf{\nabla}T_e) + Q_{ei} }[/math]
Here, [math]\displaystyle{ Q_{ei} }[/math] is a local energy transfer term between the atoms and electrons, which may or may not be combined with an external source term. See more on this and temperaturedependent electronic parameters in the related keyword eph_Tinfile
. There are twenty input keywords connected to this calculation method. For some of these keywords input may or may not be provided always. These are as follows:
eph_fdm_option
, eph_friction_option
, eph_random_option
, eph_betafile
, eph_Tinfile
, eph_box_limits
, eph_rho_e
, eph_C_e
, eph_kappa_e
, eph_Ti_e
, eph_gsx
, eph_gsy
, eph_gsz
, eph_fdm_steps
, eph_md_last_step
, eph_md_prev_time
, eph_E_prev_time
, eph_freq_Tout
, eph_freq_mesh_Tout
, eph_Toutfile
Summary
Required/optional  Type  Accepted values  Default  See also  Remarks 

Optional  Boolean  .true. or .false.

.false.

electronic_stopping

Required functionality for doing nonequilibrium MD simulations 
Example
nonadiabatic_processes = .true. eph_fdm_option = 1 eph_friction_option = 1 eph_random_option = 1 eph_betafile = 'CouplingFile.beta' eph_Tinfile = 'T_input.fdm' box_limits = 30.0 30.0 30.0 30.0 30.0 30.0 ! in Ang eph_rho_e = 1.0 eph_C_e = 3.5E01 ! in eV/K/Ang^3 eph_kappa_e = 0.12 ! in eV/K/Ang/ps eph_Ti_e = 50.0 ! in K eph_gsx = 4 eph_gsy = 4 eph_gsz = 4 eph_fdm_steps = 1 eph_md_last_step = 0 eph_md_prev_time = 0.0 ! in fs eph_E_prev_time = 0.0 ! in eV eph_freq_Tout = 10 eph_freq_mesh_Tout = 1000 eph_Toutfile = 'Tmesh.out'