Re: [Phonopy-users] Negative frequencies

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:

    Thank you for your reply. I did the 1x1x1 supercell and got negative frequencies ( higher than 2x2x1) but the negative frequencies are not at Gamma point. 

?? this does not even make sens… 1x1x1 IS ONLY ONE POINT AND IT DOES NOT DEPEND ON Q. Any fitting you would do for any Q different than zero, I will not trust it, do you know how that works? . Please read the corresponding literature on how a phonon spectra is calculated, based on your response, it seems you me that you are using Phonopy as a blackbox… no DFT either phonon calculations are blackboxes.

    You said that I have always to converge , converge what???

??... even the question I do not get it… converge what? Again, read the basic literature

    And also you said "everything depends on how the interatomic force constants extend.. and if they decay fast etc" what does it mean decay fast? And how to check if they Decay fast or not ?

Again…. 

classic papers are

X. Gonze and C. Lee, Phys. Rev. B55, 10355 (1997), especially section IX
C. Lee, X. Gonze, Phys. Rev. B 51, 8610 (1995)
S. Baroni, S. de Gironcoli, A. Dal Corso, P. Giannozzi, Rev. Mod. Phys. 73, 515 (2001).

Best Regards
    Wajood 

    > On Jan 4, 2017, at 5:04 PM, pho...@li... wrote:
    > 
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    > Today's Topics:
    > 
    >   1. phonopy-users (Shilendra Kumar Sharma)
    >   2. Re: phonopy-users (Aldo Romero)
    >   3. Re: Negative Frequencies (Aldo Romero)
    > 
    > 
    > ----------------------------------------------------------------------
    > 
    > Message: 1
    > Date: Wed, 4 Jan 2017 16:21:56 +0530
    > From: "Shilendra Kumar Sharma" <sh...@ii...>
    > Subject: [Phonopy-users] phonopy-users
    > To: pho...@li...
    > Message-ID:
    >    <a9e...@we...>
    > Content-Type: text/plain;charset=UTF-8
    > 
    > Dear PHONOPY users,
    > 
    > My system has 24 atoms(tetragonal) unit cell. I want to calculate
    > thermodynamic properties specially zero point energy. I am VASP user and
    > using DFPT (IBRION=8) method for calculating force constants.
    > 
    > I made 2*2*1 supercell from phonopy and rename SPOSCAR to POSCAR and
    > calculated force constant my INCAR is
    > 
    > SYSTEM = LVO(2 2 1)
    > ISTART = 0
    > ICHARG = 2
    > PREC = Accurate
    > ENCUT = 520.000
    > IBRION = 8
    > EDIFF = 1.0e-08
    > IALGO = 38
    > ADDGRID = .True.
    > ISMEAR = 0
    > SIGMA = 0.1
    > LREAL = Auto
    > LWAVE = False
    > LCHARG = False
    > 
    > After VASP job finishing, I calculated force constant by command
    > 
    > phonopy --fc vasprun.xml
    > 
    > It created FORCE_CONSTANTS files.
    > 
    > Now I am calculating thermal properties by command
    > 
    > phonopy -t mesh.conf
    > 
    > then it is showing message
    >       _
    >  _ __ | |__   ___  _ __   ___   _ __  _   _
    > | '_ \| '_ \ / _ \| '_ \ / _ \ | '_ \| | | |
    > | |_) | | | | (_) | | | | (_) || |_) | |_| |
    > | .__/|_| |_|\___/|_| |_|\___(_) .__/ \__, |
    > |_|                            |_|    |___/
    >                                      1.11.6
    > 
    > 
    > FORCE_SETS not found.
    >  ___ _ __ _ __ ___  _ __
    > / _ \ '__| '__/ _ \| '__|
    > |  __/ |  | | | (_) | |
    > \___|_|  |_|  \___/|_|
    > 
    > 
    > Where I am doing mistake ? My mesh.conf file is
    > 
    > DIM= 2 2 1
    > MP= 6 6 6
    > FORCE CONSTANT= Read
    > 
    > My queries are fillowing:
    > 
    > 1. How much bigger supercell we should take in account ?
    > 2. How much big KPOINTS mesh we should taken and What type ?
    > 3. In manual it iswritten we shoul take for VASP users LREAL= FALSE but
    > when I was doing calculation with LREAL=FALSE my programme was terminating
    > automaticaaly or stopping middle of the calculation. So my query is that
    > we can take LREAL= Auto.
    > 
    > Any other advice on termination of programme.
    > 
    > Thank You All PHONOPY user
    > 
    > Shilendra
    > 
    > 
    > 
    > 
    > 
    > 
    > 
    > ------------------------------
    > 
    > Message: 2
    > Date: Wed, 4 Jan 2017 12:25:23 +0000
    > From: Aldo Romero <Ald...@ma...>
    > Subject: Re: [Phonopy-users] phonopy-users
    > To: "pho...@li..."
    >    <pho...@li...>
    > Message-ID: <06F...@ma...>
    > Content-Type: text/plain; charset="utf-8"
    > 
    > It is FORCE_CONSTANTS = READ
    > No FORCE CONSTANTS!! See the underscore
    > 
    > With respect to your questions
    > 
    > 
    > 1. How much bigger supercell we should take in account ?
    > Depends? convergence with respect to supercell size is desired.. the larger the better? finally, the supercell will define the number of Q points you have calculated exactly, the others will be interpolated? for the 2x2x1, you have basically 5 points (including Gamma)? and in many systems this is not enough.. this is really system dependent
    > 
    > 
    > 2. How much big KPOINTS mesh we should taken and What type ?
    > 
    > That is a question on Electronic structure and no on Thermal properties.. depends if your system is a semiconductor or a metal.. you always have to converge with respect to Kpoints and Ecut before anything else
    > 
    >    3. In manual it iswritten we shoul take for VASP users LREAL= FALSE but
    >    when I was doing calculation with LREAL=FALSE my programme was terminating
    >    automaticaaly or stopping middle of the calculation. So my query is that
    >    we can take LREAL= Auto.
    > 
    > No.
    > 
    > 
    > 
    > ________________________________________
    > 
    > Prof. Aldo Humberto Romero
    > American Physical Society Fellow
    > Physics and Astronomy Department
    > West Virginia University
    > Phone: (304) 2936317    
    > email: alr...@ma...
    > 
    > 
    > On 1/4/17, 5:51 AM, "Shilendra Kumar Sharma" <sh...@ii...> wrote:
    > 
    >    Dear PHONOPY users,
    > 
    >    My system has 24 atoms(tetragonal) unit cell. I want to calculate
    >    thermodynamic properties specially zero point energy. I am VASP user and
    >    using DFPT (IBRION=8) method for calculating force constants.
    > 
    >    I made 2*2*1 supercell from phonopy and rename SPOSCAR to POSCAR and
    >    calculated force constant my INCAR is
    > 
    >    SYSTEM = LVO(2 2 1)
    >    ISTART = 0
    >    ICHARG = 2
    >    PREC = Accurate
    >    ENCUT = 520.000
    >    IBRION = 8
    >    EDIFF = 1.0e-08
    >    IALGO = 38
    >    ADDGRID = .True.
    >    ISMEAR = 0
    >    SIGMA = 0.1
    >    LREAL = Auto
    >    LWAVE = False
    >    LCHARG = False
    > 
    >    After VASP job finishing, I calculated force constant by command
    > 
    >    phonopy --fc vasprun.xml
    > 
    >    It created FORCE_CONSTANTS files.
    > 
    >    Now I am calculating thermal properties by command
    > 
    >    phonopy -t mesh.conf
    > 
    >    then it is showing message
    >           _
    >      _ __ | |__   ___  _ __   ___   _ __  _   _
    >     | '_ \| '_ \ / _ \| '_ \ / _ \ | '_ \| | | |
    >     | |_) | | | | (_) | | | | (_) || |_) | |_| |
    >     | .__/|_| |_|\___/|_| |_|\___(_) .__/ \__, |
    >     |_|                            |_|    |___/
    >                                          1.11.6
    > 
    > 
    >    FORCE_SETS not found.
    >      ___ _ __ _ __ ___  _ __
    >     / _ \ '__| '__/ _ \| '__|
    >    |  __/ |  | | | (_) | |
    >     \___|_|  |_|  \___/|_|
    > 
    > 
    >    Where I am doing mistake ? My mesh.conf file is
    > 
    >    DIM= 2 2 1
    >    MP= 6 6 6
    >    FORCE CONSTANT= Read
    > 
    >    My queries are fillowing:
    > 
    >    1. How much bigger supercell we should take in account ?
    >    2. How much big KPOINTS mesh we should taken and What type ?
    >    3. In manual it iswritten we shoul take for VASP users LREAL= FALSE but
    >    when I was doing calculation with LREAL=FALSE my programme was terminating
    >    automaticaaly or stopping middle of the calculation. So my query is that
    >    we can take LREAL= Auto.
    > 
    >    Any other advice on termination of programme.
    > 
    >    Thank You All PHONOPY user
    > 
    >    Shilendra
    > 
    > 
    > 
    > 
    > 
    >    ------------------------------------------------------------------------------
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    >    Phonopy-users mailing list
    >    Pho...@li...
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    > 
    > 
    > 
    > ------------------------------
    > 
    > Message: 3
    > Date: Wed, 4 Jan 2017 12:29:41 +0000
    > From: Aldo Romero <Ald...@ma...>
    > Subject: Re: [Phonopy-users] Negative Frequencies
    > To: "pho...@li..."
    >    <pho...@li...>
    > Message-ID: <761...@ma...>
    > Content-Type: text/plain; charset="utf-8"
    > 
    > It is hard to say but looking to your phonon frequencies and assuming you have not make any mistake.. they can be real? you always have to converge? did you try to calculate 1x1x1 to see if Gamma point is giving you negative values?
    > I can see that from your spectra?
    > 
    > Remember that if you get negative phonons, they could be real or they could be an artifact and you always have to check with care any property. Before doing a supercell, you should start with Gamma and check that everyting is correct and then move to a supercell?.
    > 
    > At the end, everyghint depends on how the interatomic force constants extend.. if they decay fast, a 2x2x1 could be fine but there are many systems where this is not the case?
    > 
    > 
    > ________________________________
    > Prof. Aldo Humberto Romero
    > American Physical Society Fellow
    > Physics and Astronomy Department
    > West Virginia University
    > Phone: (304) 2936317
    > email: alr...@ma...
    > 
    > 
    > From: ???? ???? ???? ???? <wd...@ka...>
    > Reply-To: "pho...@li..." <pho...@li...>
    > Date: Wednesday, January 4, 2017 at 1:10 AM
    > To: "pho...@li..." <pho...@li...>
    > Subject: [Phonopy-users] Negative Frequencies
    > 
    > Hi,
    > I have a system with 60 atoms. I've built  2x2x1 supercell using phonopy and got 240 supercell files with displacements with 240 atoms. I calculated the forces using pwscf and manged to get the bands and Dos. The problem is that i got some negative frequencies as can be seen on the attached bands and dos figures. Is there a way to get rid of these frequencies as its difficult to go to higher dimension of supercell like 3x3x1??
    > Best Regards
    > Wajood
    > 
    > 
    > Dr. Wajood A. Diery
    > Assistant Professor
    > Physics Department, Faculty of Science
    > King Abdulaziz University
    > Jeddah, Saudi Arabia
    > Email: wd...@ka...<mailto:wd...@ka...>
    > Website: http://wdairy.kau.edu.sa
    > 
    > 
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