Re: [Phonopy-users] Modulation
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atztogo
From: Atsushi T. <atz...@gm...> - 2012-10-18 16:22:19
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Hi, I have forgotten to mention one more important point, especially for non-gamma point calculation. The phase factor can be, roughly speaking, determined randomly, if the eigenvector of x element of the first atom is very small. The following procedure should be carefully considered: 1. Watch modulation.yaml first. There the complex atomic modulations are written. The real values are used for MPOSCAR. 2. Draw energy vs phase factor (e.g. 0 to 180) with fixed amplitude. And again watch modulation.yaml with respect to phase factor. 3. If the eigenmodes are degenerated, all the linear combinations can be also possible modulations. Best regards, Togo On Fri, Oct 19, 2012 at 12:33 AM, Atsushi Togo <atz...@gm...> wrote: > Hi, > > What you think is correct within harmonic approximation level. Did you > draw the curve of energy as a function of amplitude? How is the shape > of the curve? > > Best regards, > > Togo > > > On Thu, Oct 18, 2012 at 11:08 PM, Huan Tran <hu...@gm...> wrote: >> Dear all >> >> I am using phonopy (version 1.5) to calculate the phonon band of a crystal >> structure. The result is attached, showing that there is a phonon mode with >> imaginary frequencies. The q-path used in this figure is >> >> [0.500 0.000 0.500] -> [0.000 0.000 0.000] -> [0.000 -0.500 -0.500] >> -> [0.500 0.500 0.000] -> [0.000 0.000 0.000] >> >> I have chosen 2 qpoints to do modulation with various amplitudes: [0.500 >> 0.000 0.500] and [0.500 0.500 0.000] (of course, I modulated the >> structure with one q point each time). For the second q point, I did try to >> modulate with 1 and/or 2 lowest phonon modes. In all of the attempts, the >> single point calculation for any obtained MPOSCAR returns an energy which is >> ALWAYS HIGHER than the single-point calculation with MPOSCAR-orig. It is >> strange for me, because I expect that along the unstable phonon mode, energy >> has to go down, even with a single-point calculation (without relaxation). >> Is this true? Please correct me if what I expect is wrong. And please >> request me any more information if you need to help me to solve this >> problem. >> >> Thank you >> Huan Tran >> >> -- >> Dr. Huan Tran >> Assistent >> Departement Physik >> Universitaet Basel >> Klingelbergstrasse 82 >> CH-4056 Basel >> >> Tel.: +41 61 267 39 10 >> Fax: +41 61 267 37 84 >> Email: hua...@un... >> >> ------------------------------------------------------------------------------ >> Everyone hates slow websites. So do we. >> Make your web apps faster with AppDynamics >> Download AppDynamics Lite for free today: >> http://p.sf.net/sfu/appdyn_sfd2d_oct >> _______________________________________________ >> Phonopy-users mailing list >> Pho...@li... >> https://lists.sourceforge.net/lists/listinfo/phonopy-users >> > > > > -- > Atsushi Togo > http://atztogo.users.sourceforge.net/ > atz...@gm... -- Atsushi Togo http://atztogo.users.sourceforge.net/ atz...@gm... |