[Pw_forum] how to judge movement of HOMO and LUMO

[Nicola Marzari]

Dear Rajdeep,

do note that the change in the quantities CBM or VBM as you write them
below as a function of strain would not give the physical change in
CBM or VBM - as you strain the crystal, the change in CBM and VBM below
would include the physical electrostatic term, but I think they
also include an unphysical strain-dependent term that depends
on to the way the the  divergent Ewald sums that are implicitly set to
zero change as a function of strain.

This contribution might be small, but I really don't know - it's a
subtle problem, and you should really become familiar with e.g. the
calculation of work functions is done (that do not need these
subtleties) and with the theory of flexoelectricity.

				nicola


On 03/06/2014 18:42, Rajdeep Banerjee wrote:
> Dear Sclauzero  Gabriele,
>                                      I looked at the paper you suggested
> (http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.101.046405) where
> it was said that the "common reference level (phi) " is calculated as
> the "cell average of the local potential originating from the ionic
> pseudopotentials" which I guess can be calculated from the
> pseudopotentials used. Can you suggest any functional form for this
> calculation of phi ? or indicatehow to generate it from the
> pseudopotentials used?
>
> As far as I understand, after defining phi, the CBM and VBM can be
> described by:
>
>
> CBM = Ec - phi
> VBM = Ev - phi
>
> where Ec and Ev are LUMO and HOMO respectively.
>
> Thank you very much for all the help.
>
> Rajdeep Banerjee
> JNCASR,
> Bangalore, India
>
>
>
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-- 

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Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL