<html><head></head><body><div class="ydp40249a75yahoo-style-wrap" style="font-family:lucida console, sans-serif;font-size:13px;"><div><div dir="ltr" data-setdir="false">Dear All,</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">I wanted to do a calculation test using <span>PBE-functional from </span>LIBXC and compare it to the internal QE one. As a test, I opted for body centered cubic (bcc) iron.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">I'm a bit puzzled by the differences in the results.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">- First, for PBE from LIBXC, following the QE user-guide on how to use LIBXC, I put the following input: <span><b>input_dft='XC-000I-000I-101L-130L-000I-000I</b>'. I obtained a total energy value of <span>-39.08694619 Ry.</span><br></span></div><div dir="ltr" data-setdir="false"><span><br></span></div><div dir="ltr" data-setdir="false"><span>- Then, for QE internal PBE functional, after having a look to Modules/funct.f90 file, I deduced the PBE should be forced from the input as follow:<b> <span><span><b>input_dft='XC-000I-000I-003I-004I-000I-000I</b>'</span></span>.</b> Here I was quite surprised obtaining a different value of the total energy <span>-31.22123378 Ry</span>... It seems like it is not the correct PBE ?<br></span></div><div dir="ltr" data-setdir="false"><span><br></span></div><div dir="ltr" data-setdir="false"><span>- When I just use NC-PP (<span>Fe.pbe-mt_fhi.UPF) without forcing the input_dft, </span><span>I get a similar result to LIBXC-PBE ... The same result is obtained also when I forced the input_dft, but including LDA-exchange (Slater)+correlation (PW) i.e.</span> <span><span><b><span><span><b>input_dft='XC-001I-004I-003I-004I-000I-000I</b>'</span></span></b></span></span><br></span></div><div dir="ltr" data-setdir="false"><span><b><br></b></span></div><div dir="ltr" data-setdir="false"><span>I'm really confused ! I<b> </b>would be grateful if some could give a bit of explanation, on how the input_dft works exactly ? especially with respect to the Module/funct.f90 file which gives all the internal functionals. <br></span></div><div dir="ltr" data-setdir="false"><span><br></span></div><div dir="ltr" data-setdir="false"><span><br></span></div><div dir="ltr" data-setdir="false"><span>I would also ask for another issue. It is explained in the PW manuel that input_dft overrides the PP. Normally, if I'm not wrong, whatever the kind of the PP given in the input file (PBE or other; norm-conserving or ultra-soft or PAW potential), the code will discard it and does not look at it at all when input_dft is forced.</span></div><div dir="ltr" data-setdir="false"><span>Here also I'm confused, I forced the input_dft as: <span><span><span><span><b><span><span><b>input_dft='XC-001I-004I-003I-004I-000I-000I</b>'</span></span></b></span></span></span></span>, with two different PP (<span><span><span>Fe.pbe-mt_fhi.UPF</span></span></span> and <span>Fe.pbe-spn-rrkjus_psl.0.2.1.UPF</span>); and the total energies are completely different ! <b><br></b></span></div><div dir="ltr" data-setdir="false"><span><b><br></b></span></div><div dir="ltr" data-setdir="false"><span>Thanks a lot in advance<b><br></b></span></div><div><br></div><div dir="ltr" data-setdir="false">Sincerely yours.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div><div class="ydp40249a75signature"><div style="text-align:left;font-family:sans-serif;font-size:13px;" dir="ltr" data-setdir="false"><font style="font-family:lucida console, sans-serif;" size="2">=============================</font><font size="2">===========<br style="font-family:lucida console, sans-serif;"></font><div><font size="2"><font style="font-family:lucida console, sans-serif;">Dr. Abdesalem HOUARI</font></font></div><font size="2"><font style="font-family:lucida console, sans-serif;">-------------------------------------------------------------------------------------------</font><br style="font-family:lucida console, sans-serif;"><font style="font-family:lucida console, sans-serif;">Department of physics, Theoretical Physics Laboratory</font><br style="font-family:lucida console, sans-serif;"><font style="font-family:lucida console, sans-serif;"><a>University of Bejaia</a>-06000. Algeria</font><font style="font-family:lucida console, sans-serif;">.</font><br style="font-family:lucida console, sans-serif;"><font style="font-family:lucida console, sans-serif;">E-mail: <span style="text-decoration-line: underline; text-decoration-style: solid; text-decoration-color: currentcolor;"><a>abdeslam.houari@univ-bejaia.dz</a></span> & <a>habdslam@yahoo.fr</a></font><br style="font-family:lucida console, sans-serif;"><font style="font-family:lucida console, sans-serif;"><span style="text-decoration-line: underline; text-decoration-style: solid; text-decoration-color: currentcolor; background-color: rgb(0, 0, 255); font-style: italic;"></span></font><a style="font-family:lucida console, sans-serif;" href="https://sites.google.com/site/houariabdeslam/homepage" rel="nofollow" target="_blank">https://sites.google.com/site/houariabdeslam/homepage</a><br style="font-family:lucida console, sans-serif;"><font style="font-family:lucida console, sans-serif;">========================================</font><span style="font-family:lucida console, sans-serif;"></span></font><br></div></div></div></div></body></html>