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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Dear QE developers and users,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have a question in understanding occupation matrix from LDA+U output file.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>1) Definition of occupation matrix, n is:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal> n= \sum{f<psi|phi_i><phi_j><psi>}, where psi is KS eigenstates, phi_i is atomic orbital of i orbital, f is scaling factor. As i and j from phi_i and phi_j don’t have to be identical, I think it’s not guaranteed that elements in n matrix are always real… However, in the QE output, they are all shown as real numbers. In new_ns.f90, I can find that n (nr and ns) are defined as real numbers but I can’t find any restrictions other than this. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>2) While elements in the matrix are real, some of them are “negative”. How can I understand this? I found one paper about multiconfigurational character of wave functions (<a href="http://jcp.aip.org/resource/1/jcpsa6/v110/i9/p4199_s1">http://jcp.aip.org/resource/1/jcpsa6/v110/i9/p4199_s1</a> ) but it’s beyond my scope. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Did I miss something? Any suggestions and advices will truly be appreciated…<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Sincerely,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Chan-Woo<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>-------<br>Chan-Woo Lee, Ph.D.<o:p></o:p></span></i></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Postdoctoral Research Associate<o:p></o:p></span></i></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></i></p><p class=MsoNormal><i><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Department of Chemistry<br>University of Pennsylvania<br>231 South 34th Street<br>Philadelphia, PA 19104-6323 <br>Phone: 1-215-898-3564 (Office)<br></span></i><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Email: <a href="mailto:leechanw@sas.upenn.edu"><span style='color:blue'>leechanw@sas.upenn.edu</span></a> / <a href="mailto:cwandtj@gmail.com" target="_blank"><span style='color:blue'>cwandtj@gmail.com</span></a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>