[Pw_forum] A question about elphon

[songzhida]

Dear All:
I want to modify the code of ph.x to calculate phonon limited mobilities
of electrons in semiconductors.
I know ph.x can calculate phonon line-width, which contains the integral
of the electron-phonon coefficients g_{q,v}(k,i,j). And the relaxation
time can be calculated from these coefficients too:
1/\tau_{k,i} = (2\pi)/(\hbar) sum_{q,v,i} |g_{q,v}(k,i,j)|^2 (
(f_{k+q,j}+n_{q,v})\delta(e_{k,i}-e_{k+q,j}+\hbar \omega_{q,v}) ......)
The main difference between computations of phonon line-width and
relaxation time is one integrated in k-space but another in q-space.
Thus I think I need only to add some lines in subroutine elphsum() to
collect and output g_{q,v}(k,i,j) and then integrate them in q-space.
But I encounter a problem: I'm confused with some variables or functions
in elphsum():

(1) el_ph_mat(jbnd,ibnd,ik,ii), notes in the code says it means
<\psi(k+q)|dV_{SCF}/du^q_{i a}|\psi(k)>
Is u^q_{i a} a normal coordinate or the i'th descartes coordinate of
a'th atom or none of them?

(2) What is the function of symm()?
Why must g(ik,:,:) be symmetrized by it ?
Note that
g(ik,ii,jj)=CONJG(el_ph_mat_collect(jbnd,ibnd,ik,ii))*el_ph_mat_collect(jbnd,ibnd,ik,jj).

(3) I also have tried to use the following formula as
|g_{q,nu}(ik,ibnd,jbnd)|^2:
DO mu=1,3*nat
DO vu=1,3*nat
gq2(ispin,jbnd,ibnd,ik,nu)=gq2(ispin,jbnd,ibnd,ik,nu) +
DBLE(conjg(dyn(mu,nu)) * &
gq(ispin,jbnd,ibnd,ik,mu,vu) * dyn(vu,nu))
ENDDO ! vu
ENDDO ! mu
gq2(ispin,jbnd,ibnd,ik,nu)=gq2(ispin,jbnd,ibnd,ik,nu)/2/omega

where gq(ispin,jbnd,ibnd,ik,mu,vu) was gotten from:
a.
g(jbnd,ibnd,ik,ii,jj)=CONJG(el_ph_mat_collect(jbnd,ibnd,ik,ii))*el_ph_mat_collect(jbnd,ibnd,ik,jj)
......
b. map g to the whole brillouin zone, g(jbnd,ibnd,ik,ii,jj)-->
gq(ispin,jbnd,ibnd,ik,mu,vu)
......
c. symmetry gq(ispin,jbnd,ibnd,ik,mu,vu) by symm()

This process is very similar to the process of calculating phonon
line-width, the main difference is I do it for each k point. But I also
failed to get the right g_{q,v}(k,i,j).
Could you give me some advise? Thank you very much!

Regards

Zhida Song
State Key Laboratory of Electronic Thin Films and Integrated Devices,
University of Electronic Science and Technology of China,
Chengdu 610054, P.R. China
Tel:+86-28-83201475
Fax:+86-28-83204938
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20130320/343e8f34/attachment.html>