Dear Dominik,
This is the first time that I hear about negative Ueff. What I would do, I would just compute Ueff from first principles using the hp.x code of Quantum ESPRESSO: Phys. Rev. B 98, 085127 (2018). Best regards, Iurii P.S.: Please do not forget to add your affiliation when posting to the pw_forum. -- Dr. Iurii Timrov Postdoctoral Researcher STI - IMX - THEOS and NCCR - MARVEL Swiss Federal Institute of Technology Lausanne (EPFL) CH-1015 Lausanne, Switzerland +41 21 69 34 881 http://people.epfl.ch/265334 ________________________________ From: users <[email protected]> on behalf of Dominik Gresch <[email protected]> Sent: Tuesday, October 8, 2019 2:43:58 PM To: [email protected] Subject: [QE-users] Negative dr2 error in DFT+U Dear QE community, I am trying to run DFT+U calculations (lda_plus_u_kind=0) with a negative Ueff = U - J. However, this frequently results in the following error being raised: %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Error in routine mix_rho (1): negative dr2 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% I have traced this to the ns_ddot function in PW/src/scf_mod.f90, which calculates a contribution to dr2 from the Hubbard term. Due to the negative U, this value also becomes negative. Consequently, the error can be avoided by changing Hubbard_U(nt) to ABS(Hubbard_U(nt)) in this function (in two places). My question is this: - Does this change make sense, or is the sign of ns_ddot relevant? - Does it make sense physically to use negative U? These are empirical values, to match a known band structure. Thank you and best regards, Dominik Gresch
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