[DFTB-Plus-User] Troubleshooting NPT simulations using xTB in DFTB+

[Ankur Gupta]

Hi all,

I am trying to perform an NPT simulation (viz., 1 bar 50 K, 1 bar 300 K,
etc.) on a molecular cluster using DFTB+. However, for some reason, both
pressure and temperature sharply increase to very large values during the
first few time steps. The MD calculation then crashes due to SCC
not being able to converge (potentially due to crystal geometry being
unphysical). My input file is as follows,

Geometry = GenFormat {
>  <<<"TetH_dftbp_opt.gen"
> }
>
> Driver = VelocityVerlet{
>   TimeStep [fs] = 0.25
>   Thermostat = NoseHoover {
>     Temperature [Kelvin] = 50
>     CouplingStrength [cm^-1] = 3400
>     }
>     Steps = 10
>     MovedAtoms = 1:-1
>     OutputPrefix = TetH_npt
>     MDRestartFrequency = 1
>     Barostat {
>       Pressure [Pa] = 1.0E5
>       Timescale [ps] = 0.25
>       Isotropic = No
>       }
> }
> Options = {
>   TimingVerbosity = -1
>   WriteDetailedOut = No
>   RandomSeed = 589105024
> #  WriteAutotestTag = Yes
> }
> #Parallel = {
> #  UseOmpThreads = Yes
> #}
> ParserOptions = {
>   ParserVersion = 3
> }
> Hamiltonian = xTB {
>   Method = "GFN2-xTB"
>   KPointsAndWeights = SupercellFolding {
>    2  0  0
>    0  2  0
>    0  0  2
>    0.5  0.5  0.5
>   }
>   MaxSCCIterations = 500
> }


I have also attached the "md.out" file to this message. I would be happy to
provide more information if needed. I would be grateful for any help on
this issue.

Thank you.

Best,
Ankur
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