> The complete ph.x outputs are attached
You forgot to attach the output files.
> 1. Why are there 3 additional frequencies? Shouldn't there only be 3 (omega 73~75) due to the DoF of one atom?
Look at the eigenvector and see if the three "-67 cm-1 " are
translational modes.
On Wed, Mar 19, 2014 at 12:57 AM, Kan-Ju Lin <kjlin at mit.edu> wrote:
> Hi all,
>
> I am using QE 5.0.3.
>
> I am trying to test if a saddle point from the neb.x calculation is a real
> saddle point. I am doing this by looking for the vibrational frequency: If a
> state is a saddle point, it has only one imaginary (negative) frequency. If
> a state is an energy minimum, it has no imaginary frequency.
>
> My system consists of a crystal structure and a helium impurity in it. The
> crystal structures at energy minimum and the saddle point are almost
> identical, only the helium atom is displaced. To facilitate the frequency
> calculation, I used nat_todo = 1 to only allowing the helium to be
> displaced:
>
> phonons of initial state at Gamma
> &inputph
> nat_todo = 1
> tr2_ph=1.0d-14,
> prefix = "te",
> epsil=.true.,
> /
> 0.0 0.0 0.0
> 25
>
> The last line, 25, indicates only the 25th atom (helium) is displaced during
> the ph.x calculation. Because there are 25 atoms total in the system, there
> should be 75 modes. The complete ph.x outputs are attached. The energy
> minimum state has the frequencies:
>
> omega( 1) = -2.080553 [THz] = -69.399779 [cm-1]
> omega( 2) = -2.080553 [THz] = -69.399779 [cm-1]
> omega( 3) = -2.080553 [THz] = -69.399779 [cm-1]
> ..........
> ..........
> omega(73) = 4.621913 [THz] = 154.170425 [cm-1]
> omega(74) = 4.621913 [THz] = 154.170425 [cm-1]
> omega(75) = 4.621913 [THz] = 154.170425 [cm-1]
>
> with omega(4~72) all equal to zero. For the saddle point one:
>
> omega( 1) = -4.316979 [THz] = -143.998928 [cm-1]
> omega( 2) = -2.270462 [THz] = -75.734475 [cm-1]
> omega( 3) = -2.270462 [THz] = -75.734475 [cm-1]
> ..........
> ..........
> omega(73) = 2.168375 [THz] = 72.329209 [cm-1]
> omega(74) = 9.304582 [THz] = 310.367434 [cm-1]
> omega(75) = 9.304582 [THz] = 310.367434 [cm-1]
>
>
> My questions are:
> 1. Why are there 3 additional frequencies? Shouldn't there only be 3 (omega
> 73~75) due to the DoF of one atom?
> 2. Why are the three additional frequencies negative? Shouldn't there be one
> negative frequency for the saddle point, and 2 positive frequencies? and no
> negative frequency for the energy minimum?
>
> Please let me know if I understand this incorrectly, or I am missing some
> settings.
>
>
> --
> Kan-Ju Lin, Postdoctoral Associate
> MIT Materials Science and Engineering
> Office 4-053 / kjlin at mit.edu
>
>
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
--
____________________________________
Hui Wang
School of physics, Henan University of Science and Technology, Henan, China