[Pw_forum] Acousic Sum rule

[Diep Vinh Quang]

Dear all,

I am calculating the effect charge. And I using the example09 for
calculating the phonon at Gamma (q=0). The result in example09 give like
the following (SiH4):

     z*( 1)   -0.4485    0.0000    0.0000
               0.0000   -0.4485    0.0000
               0.0000    0.0000   -0.4485

     z*( 2)   -1.1347   -0.5787   -0.5787
              -0.5787   -1.1347   -0.5787
              -0.5787   -0.5787   -1.1347

     z*( 3)   -1.1347   -0.5787    0.5787
              -0.5787   -1.1347    0.5787
               0.5787    0.5787   -1.1347

     z*( 4)   -1.1347    0.5787   -0.5787
               0.5787   -1.1347    0.5787
              -0.5787    0.5787   -1.1347

     z*( 5)   -1.1347    0.5787    0.5787
               0.5787   -1.1347   -0.5787
               0.5787   -0.5787   -1.1347

I just want to ask whether this result is reasonable or not? because it
doesn't satify the Acoustic Sum Rule (Sham 1969 or Vogl 1978) in that: the
sum of the effective charge Z_{ij} over all atom = 0. In this case we can
see that it not true for the case  Z_{33}: 
Z_{33}(1)+Z_{33}(2)+Z_{33}(3)+Z_{33}(4)+Z_{33}(5)= -0.4485+ 4*( -1.1347)
differ from zero?

How can we impose this condition in the above calculation?

Thank you very much.
Vinh







-------------------------------------------------
Diep Vinh Quang
C/o Diploma Program, The Abdus Salam
International Center for Theoretical Physics(ICTP),
11 Strada Costiera, 34014, Trieste,Italy.
http://www.ictp.it