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You might want to check the 2007 JACS by Dabo et al, where we discuss the independence between adsorption energies and CO vibrational shifts; we also diagonalize the interatomic force constants obtained by finite differences on a local neighborhood.
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<div>Nicola<br>
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<div dir="ltr">Sent from a tiny keyboard... Contact info:
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<div>http://theossrv1.epfl.ch/Main/Contact</div>
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<blockquote type="cite">On 20 Feb 2020, at 01:08, ykhuang <ykhuang@dicp.ac.cn> wrote:<br>
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<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>
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<div dir="auto">Best regards. </div>
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<div dir="auto">Yike Huang. </div>
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<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>
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> start_irr = 235<br>
> last_irr = 240<br>
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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>
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-- <br>
Lorenzo Paulatto - Paris<br>
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