[gpaw-users] Ehrenfest dynamics with LCAOTDDFT?

[Toma Susi]

Dear Ask,

> On 11.07.2019, at 13:33, Ask Hjorth Larsen <asklarsen at gmail.com> wrote:
> 
> Dear Toma,
> 
> Am Do., 11. Juli 2019 um 11:57 Uhr schrieb Toma Susi via gpaw-users
> <gpaw-users at listserv.fysik.dtu.dk <mailto:gpaw-users at listserv.fysik.dtu.dk>>:
>> 
>> Dear gpaw-users,
>> 
>> I've been running Ehrenfest dynamics with the TDDFT calculator, but as you might imagine, trying to reach hundreds of fs with a near-attosecond timestep is rather painful. I was wondering whether the LCAOTDDFT calculator could be used instead to speed up the calculations.
>> 
>> The problem I run into, however, is that the EhrenfestVelocityVerlet needed for MD uses the function tddft.get_td_energy(), which is not implemented in the lcaotddft calculator. Looking at the tddft code, it seems this function calls several other functions (e.g.  td_overlap.update, td_density.update and td_hamiltonian.update), which are likewise not implemented.
>> 
>> Is there an alternative way to get the TDDFT energy in LCAOTDDFT? Or could this easily be implemented? Seems like quite a basic thing to have, but don't really know where to even start doing it myself.
> 
> There was once a push to implement Ehrenfest-LCAO-TDDFT (I was
> involved in it), but things seem to have stalled.  Some things were
> done though, and the code must exist somewhere.  There are some
> caveats since the orbitals move along with the atoms.  At least with
> real-space wavefunctions the representation doesn't change when atoms
> move.  Mikael Kuisma probably has the best overview but is on
> paternity leave.  Either way it's not entirely simple.
> 
> Best regards
> 
> Ask

Thanks – unfortunate that it is not simple, I do think it is worth implementing since GPAW is a great code for Ehrenfest.
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