Quantities defined in X_s.F

Various technical topics such as parallelism and efficiency, netCDF problems, the Yambo code structure itself, are posted here.

Moderators: Daniele Varsano, andrea.ferretti, andrea marini, Conor Hogan, myrta gruning

Quantities defined in X_s.F

Postby hplan » Sat Aug 15, 2009 10:08 am

Dear Developers:
My question is still about the response function programmed in TDDFT module of yambo.
I looked through two subroutines :O_driver.F and X_s.F, and have a confusion about quantities defined in X_s.F . Would you please do me a favor for this issue ?

I learned from X_s.F that it solves Dyson equation for $\chi$ from $\chi_0$ which is stored in X_mat. My confusion is about the last description for $\chi$:
Code: Select all
 X_mat(i1,i2,iw)=X_mat(i1,i2,iw)*4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)

As far as i know, the solution for Dyson equation should be
$\chi=(1-\chi_0\upsilon-\chi_0 f_{xc})^{-1}\chi_0$.
My question is why we need multiply a quantity like Coulomb potential
Code: Select all
4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)

for X_mat ? In this situation, does X_mat store the exact information for the response function $\chi$ ? Or other attentions need pay to ?
In O_driver.F , I found the expression the $\epsilion_M$
Code: Select all
X_epsilon(2,fr(1):fr(2))=1./(X_mat(1,1,:)*bare_qpg(iq,1)**2/Q_sq_modulus+1.)

exactly follows the formula $\epilsion_M=1/(1+\upsilon\chi)$ . Therefore, in X_s.F why we perform a more calculation over X_mat as
Code: Select all
 X_mat(i1,i2,iw)=X_mat(i1,i2,iw)*4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)


Thanks in advance!
Regards,
Hai-Ping
Hai-Ping LAN,
Department Of Electronics,
Peking University, 100871,Beijing, CHINA
hplan
 
Posts: 58
Joined: Thu Mar 26, 2009 2:26 pm

Re: Quantities defined in X_s.F

Postby myrta gruning » Fri Aug 28, 2009 11:27 am

Dear Hai-Ping,

The output of X_s, X_mat, is Chi(q,G,G') (from the solution of the Dyson equation) multiplied by 4\pi/[(q+G)(q+G')].

This quantity corresponds to a "symmetrized" inverse microscopic dielectric function \epsilon^{-1}.
I am not sure (Andrea can confirm/correct this), but I think the reason is that this quantity can be directly/conveniently used in several expressions involving the microscopic dielectric function (e.g. for the evaluation of the mass operator).

Regards,

Myrta
Dr Myrta GrĂ¼ning
Atomistic Simulation Centre
Queen's University Belfast - Northern Ireland

http://www.researcherid.com/rid/B-1515-2009
User avatar
myrta gruning
 
Posts: 303
Joined: Tue Mar 17, 2009 11:38 am

Re: Quantities defined in X_s.F

Postby andrea marini » Tue Sep 01, 2009 4:12 pm

myrta gruning wrote: I think the reason is that this quantity can be directly/conveniently used in several expressions involving the microscopic dielectric function (e.g. for the evaluation of the mass operator).


You're right. The symmetrized expression is used in the evaluation of the mass operator and of the Bethe-Salpeter kernel.
Andrea MARINI
Istituto di Struttura della Materia, CNR, (Italy)
User avatar
andrea marini
 
Posts: 447
Joined: Mon Mar 16, 2009 4:27 pm


Return to Technical Issues

Who is online

Users browsing this forum: No registered users and 1 guest

cron