<div dir="ltr">Hello, Depending on your system, it may not be necessary to use the U_RAMPING method. I was able to reproduce experimental surface energies from slab calculations for certain systems consisting of first-row transition metal atoms without using the U_RAMPING method. The paper by Dr. Matthias Krack on uranium oxide in which he used the U_RAMPING method is considered a more challenging system than first-row TM systems. Try running the calculations without U_RAMPING. Also, of your structure is not reasonable, that would also cause problems. Regards, Marco On Tuesday, April 1, 2014 10:40:09 PM UTC-4, roben nano wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr">Hi all, I am using DFT+U to relax a defective surface system. Specifically, I am using theDFT+U method MULLIKENn. However, the following warning appears when computing: *** 04:19:11 WARNING in dft_plus_u:mulliken :: DFT+U energy contibution *** *** is negative possibly due to unphysical Mulliken charges. Check your *** *** input, if this warning persists or try a different method! - I try to converge the initial SCF run with U=0eV firstly and then try to restart with DFT+U. but the same problem appears. - Using U_RAMPING [eV] 0.1 and INIT_U_RAMPING_EACH_SCF did not help. ............ &KIND Zn BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q12 &DFT_PLUS_U EPS_U_RAMPING 1.0E-3 U_MINUS_J [eV] 2.0 L 2 U_RAMPING [eV] 0.7 &END DFT_PLUS_U &END KIND .................................. Thanks a lot for the attention, best regards, </div></blockquote></div>