[QE-developers] Static density response and xc kernels

[Iurii TIMROV]

Dear Jacob,


> d^2E_xc / drho(r) drho(r’)


This is dV_xc/drho which is the second term in Eq. 13 in PRB 88, 064301 (2013). Equations 12 and 13 of this reference are implemented in the routine LR_Modules/dv_of_drho.f90


> chi(r,r’, omega=0) = drho(r)/dv(r’)


The response charge density drho is computed in the routine LR_Modules/incdrhoscf.f90


In the TDDFPT codes in QE the density-density response is computed using the Lanczos or Davidson algorithm, see e.g. Eq. 17 in the aforementioned paper.  See also Eq. 3 in PRB 102, 035156 (2020).


HTH


Greetings,

Iurii


--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: developers <developers-bounces at lists.quantum-espresso.org> on behalf of Jacob Williams <jacob.z.williams at duke.edu>
Sent: Monday, May 9, 2022 7:48:00 PM
To: developers at lists.quantum-espresso.org
Subject: [QE-developers] Static density response and xc kernels

Dear all,

I am working on implementing the LOSC correction for DFT (see, e.g., arXiv:2202.01870) in QE 7.0, and am in need of calculating the zero-frequency density-density response [chi(r,r’, omega=0) = drho(r)/dv(r’)] (or its plane-wave representation), as well as the exchange-correlation kernel [d^2E_xc / drho(r) drho(r’)]. Note that I’ve suppressed spin indices.

Is this possible to do with existing routines? I know the capability must exist, because more powerful versions (the full frequency-dependent response) are used by TurboEELS and co, but I haven’t been successful in finding how to compute the static quantities in the code. I thought the response function might be obtainable from the Kohn-Sham responses dpsi obtained from LR_Modules/response_kernels.f90, but I’m not sure how to connect that to the full response function.

Thank you in advance for your time and your help!

Sincerely yours,

Jacob Williams
PhD candidate, Weitao Yang group
Duke University Department of Chemistry
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