<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body dir="auto"><div dir="auto">Hello Paulatto,</div>Thank you for your patient answer. <div dir="auto">Actually in the slab system, the absorption is very weak. Even it is possible that the absorption is still overestimated. So I think it makes sense to treat CO as a decoupled part.</div><div dir="auto">I'll try to calculate the entire matrix or find other ways.<br><div dir="auto">Thank you again. </div></div><div dir="auto"><br></div><div dir="auto">Best regards. </div><div dir="auto"><br></div><div dir="auto">Yike Huang. </div><div><br></div><div style="font-size:100%;color:#000000" dir="auto"><!-- originalMessage --><div>-------- 原始信息 --------</div><div>发件人： Lorenzo Paulatto <paulatz@gmail.com> </div><div>日期: 2020/2/20 03:33 (GMT+08:00) </div><div>收件人： users@lists.quantum-espresso.org </div><div>主题： Re: [QE-users] What's representation 0 in ph.x? </div><div><br></div></div>> start_irr = 235<br>> last_irr = 240<br><br>Hello,<br>I did not understant that the molecule was adsorbed on a surface! In <br>this case it makes sense to compute several q-points (not orthogonal to <br>the surface!) However, if you set start_irr and last_irr, you are only <br>computing a few rows of the dynamical matrix. As the phonons are the <br>square roots of the eigenvalues of this matrix, you need the entire <br>matrix in order to compute them.<br><br>You can compute differents irreducible representations (irr) separately <br>and then combine the results together as explained in the Grid_example <br>of phonon. But you still need all the matrix. If you have reason to <br>think that the CO vibration is completely decoupled from the rest of the <br>system, you may try to get its vibrational frequency by doing finite <br>differences. It would also be possible to modify phonon to only compute <br>the minor of the dynamical matrix that involve CO, then diagonalize it, <br>but it is not currently implemented.<br><br>hth<br><br>-- <br>Lorenzo Paulatto - Paris<br>_______________________________________________<br>Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)<br>users mailing list users@lists.quantum-espresso.org<br>https://lists.quantum-espresso.org/mailman/listinfo/users<br></body></html>