<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body dir="auto"><div dir="auto">I'm sorry for attaching Luiz's mail by mistake. I re-write my mail. Really sorry.</div><div dir="auto"><br></div>Hi, QE users.<div dir="auto"><div dir="auto" original_font_attr="-1" original_line_height_attr="">Recently I plan to perform free energy calculations of CO absorption using ph.x, matdyn.x, q2r.x and fqha.x. However, I meet mainly 2 problems.</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">1. When I do phonon calculation of isolated CO molecule with q points sampling automatically 2x2x2, I find large negative frequency emerges in DOS. </div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Could anyone tell me why ph.x yields negative frequency? Moreover if I want to eliminate the negative frequency, should I decrease the tr2_ph value?</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">2. When I do phonon calculation of the CO absorbed slab, to simplify the calculation, I set start_irr and last_irr parameters including three translational degrees of freedom of C and O atom. However, after each q point iteration, ph.x outputs one line like:</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Not Davison diagonalization, representation 0 is not done.</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">As a result, no frequency information is yielded, although ph.x job terminates normally. However, it is hard to understand representation 0, because irreducible representation in ph.x is marked from 1, not 0. I don't know how I can solve this problem.</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Any suggestions will be appreciated. </div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Best regards.</div><div dir="auto"><br></div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Yike Huang</div><div dir="auto" original_font_attr="-1" original_line_height_attr="">PhD candidate.</div><div dir="auto" original_font_attr="-1" original_line_height_attr="">Dalian Institute of chemistry and physics, CAS, China.</div></div></body></html>