Hello everyone, I was wondering if anyone in the forum got a chance to have a look at my issue. Any help is appreciated.
Thanks, -Navaneeth On Mon, Feb 9, 2015 at 4:10 PM, Navaneetha Krishnan <[email protected]> wrote: > Forgot to attach my IFC file. Please find si.555.fc attached with this > email. > > Thanks, > -Navaneeth > > On Mon, Feb 9, 2015 at 3:45 PM, Navaneetha Krishnan <[email protected] > > wrote: > >> Hello Quantum Espresso users, >> >> I am trying to use QE to get the real space harmonic force constants >> using pw.x, ph.x and q2r.x in the same order for Si. I have attached all my >> input files. I am using a 5X5X5 mesh. >> >> I used ibrav=0 and my lattice vectors are [0 0.5 0.5], [0.5 0 0.5], [0.5 >> 0.5 0] in alat units. So if I understand the convention given in the faq >> phonon section of the documentation, the first nearest neighbors should >> have the indices [1 1 1], [5 1 1], [1 5 1] and [1 1 5]. >> >> From my understanding, the first nearest neighbours for Si have the >> diagonal term in the force constant matrix +/- alpha and off-diagonal term >> in the force constant matrix +/- beta for some alpha and beta. >> >> Now, the [1 1 1] force constant seems to have the right symmetries : >> atom pair : 1 2 >> 148 1 1 1 -6.40122756000E-02 11 >> 652 1 1 1 -4.29620484800E-02 12 >> 1156 1 1 1 -4.29620484800E-02 13 >> 1660 1 1 1 -4.29620484800E-02 21 >> 2164 1 1 1 -6.40122756000E-02 22 >> 2668 1 1 1 -4.29620484800E-02 23 >> 3172 1 1 1 -4.29620484800E-02 31 >> 3676 1 1 1 -4.29620484800E-02 32 >> 4180 1 1 1 -6.40122756000E-02 33 >> >> However, the [5 1 1] (and [1 5 1], [1 1 5]) force constants do not have >> the right symmetries >> atom pair : 1 2 >> 152 5 1 1 -3.87971851534E-03 11 >> 656 5 1 1 1.05471196450E-03 12 >> 1160 5 1 1 1.05471196450E-03 13 >> 1664 5 1 1 1.05471196450E-03 21 >> 2168 5 1 1 -3.60176689065E-04 22 >> 2672 5 1 1 -3.96403112877E-04 23 >> 3176 5 1 1 1.05471196450E-03 31 >> 3680 5 1 1 -3.96403112877E-04 32 >> 4184 5 1 1 -3.60176689065E-04 33 >> >> *The first column is the line number in my file, then followed by the >> three indices for the lattice vectors, then the force constant and then >> finally the component (11=xx, 12=xy and so on)* >> >> Does anyone have an idea why this happens? >> >> P.S. : In the si.scf.in file, I have CELL_PARAMETERS {cubic}. I have >> also tried with CELL_PARAMETERS {alat} and there is no difference. >> >> Thanks, >> Navaneeth >> -- >> Navaneetha Krishnan Ravichandran, >> Graduate Student, >> Mechanical Engineering, >> Caltech. >> > > > > -- > Navaneetha Krishnan Ravichandran, > Graduate Student, > Mechanical Engineering, > Caltech. > -- Navaneetha Krishnan Ravichandran, Graduate Student, Mechanical Engineering, Caltech.
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