The reason of negative frequencies are : 1. Look you pseudopotential perhaps use another and see. 2. Your structure is not well optimized.
and many... wishes sanjeev On Sun, Dec 13, 2015 at 8:02 PM, Barnali Bhattacharya < [email protected]> wrote: > Dear Sir/Madam > > > > I am a quantum espresso user and interested in phonon calculation of BN > doped two dimensional system. For these first of all I have checked the ecut > off convergence and taking this ecutwfc value checked the K-point > convergence. After taking this ecutwfc and k-point value, I have optimized > the structure with ‘VC-relax option’ with convergence criteria > > “etot_conv_thr = 1.0D-16, > > forc_conv_thr = 1.0D-16,”. > > > > Taking the relaxed position and cell parameter I have checked the suitable > lattice constant for which energy is minimum by using the script… > > > > …………………………………………… > > #!/bin/sh > > ……………. > > ………… > > ………… > > for a in `seq -w 0.995 0.001 1.005 ` > > do > > ………………………….. > > ………… > > ………………. > > cat > $MOL.$a.in << EOF > > &control > > calculation='relax', > > restart_mode='from_scratch', > > …………………. > > ………………. > > …………….. > > ………………… > > / > > CELL_PARAMETERS alat > > `echo $a*12.901074275 | bc -l` 0.000000000 0.000000000 > > `echo $a*6.45053713| bc -l` `echo $a*11.1726581| bc -l` 0.00000 > > 0.000000000 0.000000000 29.000000000 > > ATOMIC_SPECIES > > C 12.0107 C.pz-n-rrkjus_psl.0.1.UPF > > ATOMIC_POSITIONS (crystal) > > ............................. > > …………………………………….. > > ………………………………….. > > ……………………………… > > ………………………………… > > ………………………………….. > > …………………………………………………………………………………………………………………………………………………………………… > > > > Then taking the lattice constant for which energy is minimum and the > atomic position we have calculated phonon dispersion curve, but found > negative frequency. > > > > I am confused is there any mistake in my procedure. > > > > Could anyone please guide me how this negative frequency will be > disappear? Any help will be thankfully acknowledged. > > > > Thanking you. > > > > Sincerely > > Barnali Bhattacharya > > Ph.D student > > Department of physics > > Assam University > > > > > > > > > > <https://www.avast.com/lp-safe-emailing?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> > This > email has been sent from a virus-free computer protected by Avast. > www.avast.com > <https://www.avast.com/lp-safe-emailing?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> > <#1519ea7e51a8ace0_DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- With Best Regards, ------------------------------------ Dr. Sanjeev Kumar Gupta Fulbright Post-Doctoral Scholar Dept. of Physics Michigan Technological University 1400 Townsend Drive, Houghton MI 49931, USA ------------------------------------
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