Re: [Phonopy-users] Negative frequencies for FCC Al

[eric h. <er...@vi...>]

Thank you Eugene. I will have to look through them.
Thank you,
Eric

On Sun, Jul 30, 2017 at 6:27 PM Roginskii Eugene <rog...@ho...>
wrote:

> Hi Eric,
> I wrote two python scripts for:
> 1. Optimization of structure (cellopt.py)
> 2. calculation of supercell force set to plot phonon dispersion branches.
>
> Both attached.
> The first one request POSCAR.in file to be in the same directory with
> structure parameters in VASP format, output is POSCAR.fin (this file should
> be additionally symmetrized because ase optimization technique breaks the
> symmetry). The second script requires POSCAR as input geometry and proper
> setup of variables:
> kmesh=[3,3,3]  # k-point mesh
> Ecut=900 # Cutoff Energy eV
> XCF='LDA' # Exchange-correlation
> LOG='disp.log'
> PrimMatrix=[[1.0, 0.0, 0.0], [0.0, 1.0, 0.0],  [0.0, 0.0, 1.0]]
> DIM=[[2,0,0], [0,2,0], [0,0,2]]
>
> The resulting data are in files  disp.yaml  FORCE_SETS. These files plus
> POSCAR (as input scturcture) is pretty enough to plot the phonon band
> structure using phonopy python script. See MgO directory example of PHONOPY
> package.
>
> I've tested my scripts for nitride wurzite and the draft result seems to
> be reliable with GPAW calculator. I would recommend to try GPAW calculator
> first for your system and than switch to EMT.
>
>
> Eugene
>
>
>
> On 07/27/2017 06:08 PM, eric hoglund wrote:
>
> Hi Eugene,
> I am still a novice at all of this, so thank you for any help you can
> provide. I am using phonopy as a puthon module. After declaring the force
> set "phonopy.set_forces(...)" i have now symetrisized the force constant
> with the built in comand. This didn't solve the issue.
> For the calculator, I am trying to install abinit, but I am on windows so
> it's tricky. EMT seems to work on ase.phonon so the calculator shouldn't be
> the issue (i think?)
> Thank you
> Eric
>
> On Thu, Jul 27, 2017 at 6:45 AM Roginskii Eugene <rog...@ho...>
> wrote:
>
>> Hi,
>> This is most probably calculator issue. I don't know how EMT acts, but
>> maybe there are some additional parameters needed like cutoff energy or
>> k-points mesh. Moreover sometimes it is worth to apply acoustic sum rule
>> (FC_SYMMETRY option of PHONOPY).
>>
>> Eugene.
>>
>> On 07/27/2017 04:59 AM, eric hoglund wrote:
>>
>> Dear users,
>>
>> I have been attempting to model the phonon dispersion of FCC aluminum,
>> which should be a fairly simple task. I would like to use phonopy instead
>> of ase's phonon module due to some additional features. When plotting, all
>> of my acoustic bands appear negative, any ideas why? I have read online in
>> different locations that this is due to instability or poor potentials.
>> But running this in other software produces positive frequencies (and
>> acoustic should be stable for relaxed fcc aluminum). I have followed a
>> process similar to the Si-8.py example, but I have removed the 0.25&0.75
>> basis to make it FCC instead of diamond. In addition I am using the EMT
>> calculator supplied by ASE. My file is attached.
>>
>> Other short questions:
>> -when I use a supercell>7x7x7 the system seems to lock up on creating the
>> primitive vectors. If it passed that it will lock up on getting the force
>> constant. Is this just an efficiency thing? ASE's phonon portion doesn't
>> seem to have the same issue.
>>
>> Thank you,
>> Eric Hoglund
>> University of Virginia
>> PhD student
>> 1(919)538-1536 <%28919%29%20538-1536>
>>
>>
>> ------------------------------------------------------------------------------
>> Check out the vibrant tech community on one of the world's most
>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>>
>>
>>
>> _______________________________________________
>> Phonopy-users mailing lis...@li...://lists.sourceforge.net/lists/listinfo/phonopy-users
>>
>>
>>
>> ------------------------------------------------------------------------------
>> Check out the vibrant tech community on one of the world's most
>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>> _______________________________________________
>> Phonopy-users mailing list
>> Pho...@li...
>> https://lists.sourceforge.net/lists/listinfo/phonopy-users
>>
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>
>
>
> _______________________________________________
> Phonopy-users mailing lis...@li...://lists.sourceforge.net/lists/listinfo/phonopy-users
>
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Phonopy-users mailing list
> Pho...@li...
> https://lists.sourceforge.net/lists/listinfo/phonopy-users
>