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[Z_Lin <applelinux@gmail.com>]

Hi, Matthieu,

Thanks for your prompt reply. I will try to follow you recipes to find
the matrix element. If I understand correctly, the matrix element is
calculated through the ground state wavefunction at least for getting
the lamda (e-p constant). So if the system is excited by a laser
pulse, can the matrix element be the same? I mean, since the screen
potential is from the fact that the electrons react to contribute to
the effective potential. Wouldn't this effective potential change when
the electrons are excited in terms of non-zero electron temperatures,
temperature dependent? This sounds that one has to do calculation of
the wavefunctions at conditions of non-zero electron temperatures. And
here comes another questions while I was reading your previous email
about the physical electron temperature tphysel and the laser paper by
CEA group PRL 2006.  I assume that they specify the value of tphysel
to be 6eV in abinit?

BTW, the umklapp processes is included in the calculations of matrix element?

Thanks!  I found this forum very useful and informative. You guys are
doing a great job!

Cheers,
Zhibin

Here I cited your previous email in Dec21 2007

" >Whenever somebody asks this question, the PRL 2006
 which one? By the CEA gang? (hello boys!)

 >(laser irradiation paper) is good example. They used the smearing more
 >than 6 eV. It is reasonable only when the observable time is less than
 >the time of electron -ion interaction. Am I right ?
 That depends what you want to calculate: if you are looking for the
 effects of laser irradiation, you may want to see the energy transfer to
 the lattice, so you would start with excited electrons and then see where
 the energy goes. I'm not sure this is possible with abinit, unless you
 specify the occ by hand, and then you still need a method to evolve the
 occupation numbers, which is not coded. This has been done in the
 literature with other codes though."

 On Wed, Feb 13, 2008 at 9:54 AM, Matthieu Verstraete <mjv500@york.ac.uk> 
wrote:
>
> Hello,
>
>
> > I was reading the archives in the forum. From your email, it sounds like 
> > it
> > is not possible in abinit to calculate the e-ph matrix element for
> > transitions of electrons states which are not on Fermi surface.
> By default the elphon matrix elements are integrated over the Fermi
> surface, as defined by the input eigenvalues and fermi energy. For an
> insulator you will get 0 everywhere.
>
>
> > For example, the electrons could be excited by laser and lead to a wide
> > distribution of occupations around Fermi level. I have limited
> > experiences using abinit. Maybe this has been implemented?
> 2 things are possible:
>
> 1) you can increase the smearing temperature in the anaddb run. This will
> mimick the population being smeared out. If T is large enough you will
> occupy the conduction band and the matrix elements will be non zero
>
> 2) The other possibility is to fix the fermi energy (for the elphon part)
> by hand with the elph_fermie variable to anaddb
> (http://www.abinit.org/Infos_v5.5/users/anaddb_help.html#elph_fermie)
>
> This means you are calculating the coupling between the
> phonons and the electrons which are at that energy.
>
> The feature has never been tested, even though the implementation is
> simple. Use at your own risk!
>
> The energy reference for elph_fermie is the same as the band energies in
> the GS part, so if you set elph_fermie = the fermi energy from the ground
> state run (to all digits) you will get the same result as if you do not
> set elph_fermie.
>
> Please report any success or problems to the forum: I am very interested!
>
> Matthieu
>