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 $\chi$:
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X_mat(i1,i2,iw)=X_mat(i1,i2,iw)*4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)
$\chi=(1-\chi_0\upsilon-\chi_0 f_{xc})^{-1}\chi_0$.
My question is why we need multiply a quantity like Coulomb potential
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4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)
In O_driver.F , I found the expression the $\epsilion_M$
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X_epsilon(2,fr(1):fr(2))=1./(X_mat(1,1,:)*bare_qpg(iq,1)**2/Q_sq_modulus+1.)
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X_mat(i1,i2,iw)=X_mat(i1,i2,iw)*4.*pi/bare_qpg(iq,i1)/bare_qpg(iq,i2)
Regards,
Hai-Ping