[DFTB-Plus-User] TD-DFTB

[Franco Bonafé]

Dear Roozbeh Anvari,

The warning comes because you are using a periodic structure, and the
currently implemented dipole coupling only works either for non-periodic
structures, or when the electric field is polarized in non-periodic
directions (e.g., directions in which the geometry has a large vacuum
region between periodic images). In your case, for example, your field's
polarization vector is (0,1,0), and judging by the number of k-points that
you are using in your sampling, I guess your structure is really periodic
in the (0,1,0) direction. Hence, this would not give physically meaningful
results. If you are dealing with a slab that is, for example, parallel to
the xy plane, then you could polarize your electric field in the (0,0,1)
direction. We plan to implement other coupling methods to the Hamiltonian,
which will allow for laser fields polarized in periodic dimensions, but
this is currently not possible.

The error message is something completely different, namely due to your
attempt to run Ehrenfest (ion) dynamics in periodic systems sampling
several k-points. This is not implemented yet and then it's not possible.
An alternative would be to use a supercell that allows you to run a Gamma
point-only calculation, for which ion dynamics in principle works.

Best regards,
Franco


El jue, 17 feb 2022 a las 11:35, Roozbeh Anvari (<roozbeh.anvari at gmail.com>)
escribió:

> Dear DFTB+ community,
>
> I am wondering why I am getting the following warning and error message,
>
> Thank you for your help,
> Roozbeh Anvari
> PDF, Physics, Queen's University , Canada
>
>
> WARNING!
> -> Polarization components of the laser in a periodic direction do not
> work.  Make sure you are polarizing the field in non-periodic directions.
> ERROR!
> -> Ion dynamics is not implemented yet for imaginary Hamiltonians.
> ERROR STOP
>
> ----------------------------------------------
>
> Geometry = GenFormat {
>   <<< coords.gen
> }
>
> Driver = {}
> Hamiltonian = DFTB {
>   SCC = Yes
>   SCCTolerance = 1e-8  # default : 1e-5
>   MaxAngularMomentum = {
>     C = "p"
>  }
>   Filling = Fermi {
>     Temperature [Kelvin] = 100
>   }
>   SlaterKosterFiles =   {
>   C-C="../pbc-0-3/C-C.skf"
>   }
>
>   KPointsAndWeights = SuperCellFolding {
>     20 0 0
>     0 20 0
>     0 0 1
>     0.5 0.5 0.0
>   }
>
>   Dispersion = LennardJones{
>    Parameters = UFFParameters{}
>   }
> }
>
> InputVersion = 21.2
> ElectronDynamics = {
> Steps = 50000
> TimeStep = 0.1
> FieldStrength [v/a] = 0.01
> Perturbation = Laser {
> PolarizationDirection = 0 1 0
> LaserEnergy [ev] = 2.55
> }
> EnvelopeShape = Sin2 {
> Time1 [fs] = 30.0
> }
> Populations = Yes
> IonDynamics = Yes
> InitialTemperature [k] = 0.0
> Pump = Yes
> PumpProbeFrames = 1000
> PumpProbeRange [fs] = 0.0 50.0
> EulerFrequency = 200
> }
>
>
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-- 
Dr. Franco P. Bonafé
*http://francobonafe.weebly.com <http://francobonafe.weebly.com>*
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