[Pw_forum] TDDFT approach for periodic system

[O. Baris Malcioglu]

Dear All,
The current implementation of TDDFPT in Q-E is intended for "standalone"
systems (i.e. non bulk, solvated or encapsulated in dielectric systems are
ok). You will see confinement effects in lower dimensional systems
(including 1D and 2D systems) in the non-extended dimensionality(-ies) save
excitations with strong Mott-Wannier like character (CT excitations in
theoretical chemistry) since the oscillator strength for them in the current
implementation goes to zero due to ALDA (working on that). For the extended
dimensions you'll see no accountable difference from run-of-the-mill DFT-RPA
save if there is an extraordinarily strongly bound exciton at gamma point
(i.e. strongly ionic materials) (please see how TDDFT is formulated through
response -charge-, and how K points may come into play). For "ordinary" bulk
materials, frequency dependence and long range tail of the kernel is
generally mandatory for a bound exciton, which is quite "tricky" to add I
would say (beware of EXX and TD-HF, they tend to have quite wrong exciton
binding energies, personally I think this is due to lack of inclusion of a
proper generalised dielectric function in their formulation).  If you want
to study "ordinary bulk materials" I would recommend you BSP or TD-CFT
whenever GW can not save the day. Did you try SAX?
Best,
Baris
P.S.
(There are many books on the topic, especially regarding what to expect and
what not to expect from TDDFT, my personal opinion is that TDDFT thrives in
the realm between theoretical chemistry and bulk materials, i.e. large
molecules, nanocrystals, etc. Then again, this is my personal opinion)
I would recommend you to start with M.A.L. Marques, C.A. Ullrich, F.
Nogueira, A. Rubio, K. Burke, and E.K.U. Gross (eds.), Time-Dependent
Density Functional Theory (Springer-Verlag, 2006). )

2011/4/20 Giuseppe Mattioli <giuseppe.mattioli at mlib.ism.cnr.it>

> Dear all
> I did not say that TDDFPT does not work with periodic system, but you
> cannot
> have a realistic absorption spectra of a slab (or bulk crystal) if you
> sample
> the Brillouin zone by using Gamma only... TDDFPT works fine with finite
> systems, i.e., which do not show a (strong) k dependence of the psi_n,k
> eigenvalues.
>
> Giuseppe
>
> On Wednesday 20 April 2011 03:00:41 Johari, Priya Sudhir wrote:
> > Thanks Marton, its working.
> >
> > On Tue, Apr 19, 2011 at 5:40 PM, Marci <vormar at gmail.com> wrote:
> > > Dear Priya,
> > >
> > > Though I have never tried, it should work with periodic systems if you
> > > sample the Brillouin zone only with the gamma point. Keep in mind that
> > > the usual adiabatic approximations with (semi)local functionals might
> > > not work very well for calculating the absorption of periodic systems.
> > >
> > > Marton
> > >
> > > --
> > > Marton Voros
> > > PhD student
> > > Department of Atomic Physics
> > > Budapest University of Technology and Economics
> > > Budafoki út 8., H-1111, Budapest, Hungary
> > > www.fat.bme.hu/MartonVoros
> > >
> > > On Tue, Apr 19, 2011 at 11:02 PM, Johari, Priya Sudhir
> > >
> > > <priya_johari at brown.edu> wrote:
> > > > Thanks Duy, but the link does not give sufficient information.
> However,
> > > > I found a discussion on forum's archive itself where Giuseppe
> Mattioli
> > > > has mentioned that TDDPFT does not work for periodic systems :-(
> > > >
> > > > Dr Priya Johari.
> > > > Brown University,
> > > > Providence, RI - 02906. USA
> > > >
> > > > On Tue, Apr 19, 2011 at 3:59 PM, Duy Le <ttduyle at gmail.com> wrote:
> > > >> If you do a little homework (such as googling keyword TD-DFPT),
> you'll
> > > >> find this link
> > > >> http://qe-forge.org/projects/tddfpt/
> > > >> I have not read it carefully but I guess it contains some useful
> > > >> information.
> > > >> --------------------------------------------------
> > > >> Duy Le
> > > >> PhD Student
> > > >> Department of Physics
> > > >> University of Central Florida.
> > > >>
> > > >> "Men don't need hand to do things"
> > > >>
> > > >>
> > > >>
> > > >> On Tue, Apr 19, 2011 at 3:26 PM, Johari, Priya Sudhir
> > > >>
> > > >> <priya_johari at brown.edu> wrote:
> > > >> > TD-DFPT
> > > >>
> > > >> _______________________________________________
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>
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>    Giuseppe Mattioli
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