===== MDET =====

In the Fireball code, it is possible to perform nonadiabatic molecular dynamics (MDET). The method which is implemented here belongs to the group of semi-classical techniques based on trajerctories. The method use Tully's fewest switching method ref: J.C.Tully, JCP 93, 1061 (1990). MDET simulations is switch on by flag imdet=1 in fireball.in. Ionic integration time step has a value dt = 0.5 fs. Integration time step of the electrons is denoted nddt = 100 and its optimal value is 100 which means hundreth of MD ions step. In this particular case it is 0.005fs.

Here is an example of fireball.in:

==== fireball.in : ====
<code>
&option
iensemble = 1
iquench = 0
nstepi = 1
nstepf = 500
icluster = 1
dt = 0.5
T_initial = 300.0
tempfe = 200.0d0
imdet = 1
nddt = 100
iProjWF = 0
&end
&output
iwrtxyz     = 1
iwrteigen   = 1
iwrtewf     = 0
&end
</code>

For the simulation the input.mdet file is necessary to place into working directory as well. The first option means if the analytical or numerical nonadiabatic term will be calculated. The analytical one is the most memory consuming and for system above 200 Si atoms needs about 90 Gb, depending on basis. The second option allows to automatically create electron hole pair. In this case the user should offer the file with wavefunction of the electrone and hole. The third option Allow to perform do the scf in ground state or in excite state. In the systems where excited state is degenerated and the system would not converge. In this case it is convenient to do ground state scf, although the forces will be calculated from excited state. The last choice is the number of the orbitals which should be evolved in time and its occupations. 

Here is an example of mdet.input:

==== mdet.input : ====

<code>
0                     ! analytical nonadiabatic term = 0 ; numerical nonadiabatic term = 1
0                     ! do you want to make occupancy automaticaly? if yes offer the wf of electrone and hole
1                     ! are you doing GS scf ?
300                   ! tempfe_eh
4                     ! number of wf stored in history
1.0                   ! weights of reference functions
0.0
0.0
0.0
4                     ! nele (number of states where switches are possible)
65  2.0
66  1.0
67  1.0
68  0.0
</code>

{{:MDET-structure.png}}

{{:MDET-chart.png}}