Dear Lihui Ou, oulihui666 wrote: > Dear all, > Recently, I have been performing calulation of frequency and zero > point energy of CO2 molecule. However, unfortunately, I have > obtained negative frequency. According to the manual, there are several
> ibrav = 1, > celldm(1) = 15.11781502, This seems too small. You want to avoid spurious interactions between periodic replicas of the molecule. > nat = 3, > ntyp = 2, > ecutwfc = 26 , > ecutrho = 260 , These cut-offs may also be too small. C and O have 2p electrons which are hard to deal with PWs, even with US PPs. > occupations = 'smearing' , > degauss = 0.02 , This is too large for a molecule, you can use much smaller values. > &ELECTRONS > conv_thr = 1.D-12 , This requirement may be too strict. Anyway, if you don't have problems in convergence you can keep it as it is. > (2) Performing scf calculations: > &CONTROL > calculation = 'scf' , > restart_mode = 'from_scratch' , > outdir = '/home/olh/tmp/' , > pseudo_dir = '/home/olh/pseudo/' , > prefix = 'CO2' , > / > &SYSTEM > ibrav = 1, > celldm(1) = 15.11781502, > nat = 3, > ntyp = 2, > ecutwfc = 26 , > ecutrho = 260 , > occupations = 'smearing' , > degauss = 0.02 , > smearing = 'methfessel-paxton' , > nspin = 2 , > starting_magnetization(1) = 0.5, > starting_magnetization(2) = 0.5, > / > &ELECTRONS > conv_thr = 1.D-12 , > mixing_beta = 0.4D0 , > / > ATOMIC_SPECIES > C 12.01100 C.pbe-rrkjus.UPF > O 15.99940 O.pbe-rrkjus.UPF > ATOMIC_POSITIONS angstrom > C 4.000000000 4.000000000 4.000000000 0 0 0 > O 5.172018724 4.000000000 4.000000000 0 0 0 > O 2.827981276 4.000000000 4.000000000 0 0 0 > K_POINTS automatic > 16 16 16 1 1 1 Maybe I don't understand what you want to calculate, but I don't see any need of a k-point sampling when computing an isolated molecule. Why don't you use gamma as in the relax calculation? > > (3) Performing frequency calculation using PHONOS codes: > phonons of CO2 at Gamma > &inputph > tr2_ph=1.0d-20, This is very strict! > prefix='CO2', > epsil=.false., > amass(1)=12.0110, > amass(2)=15.9994, > outdir='/home/olh/tmp/', > fildyn='CO2.dynG', > / > 0.0 0.0 0.0 > Finally, I obtained the frequency of CO2 molecule, output file as follows: > Convergence has been achieved > Number of q in the star = 1 > List of q in the star: > 1 0.000000000 0.000000000 0.000000000 > Diagonalizing the dynamical matrix > q = ( 0.000000000 0.000000000 0.000000000 ) > ************************************************************************** > omega( 1) = -3.661345 [THz] = -122.130124 [cm-1] > omega( 2) = -3.661345 [THz] = -122.130124 [cm-1] > omega( 3) = 3.659957 [THz] = 122.083850 [cm-1] > omega( 4) = 7.879986 [THz] = 262.849774 [cm-1] > omega( 5) = 7.879986 [THz] = 262.849774 [cm-1] > omega( 6) = 19.746862 [THz] = 658.688787 [cm-1] > omega( 7) = 19.746862 [THz] = 658.688787 [cm-1] > omega( 8) = 38.945041 [THz] = 1299.075383 [cm-1] > omega( 9) = 70.000609 [THz] = 2334.984491 [cm-1] > ************************************************************************** > Mode symmetry, D_4h(4/mmm) point group: > omega( 1 - 2) = -122.1 [cm-1] --> E_g X_5 M_5 R > omega( 3 - 3) = 122.1 [cm-1] --> A_2u X_4' M_4' I > omega( 4 - 5) = 262.8 [cm-1] --> E_u X_5' M_5' I > omega( 6 - 7) = 658.7 [cm-1] --> E_u X_5' M_5' I > omega( 8 - 8) = 1299.1 [cm-1] --> A_1g X_1 M_1 R > omega( 9 - 9) = 2335.0 [cm-1] --> A_2u X_4' M_4' I > ************************************************************************** > PHONON : 1h48m CPU time, 2h25m wall time > ...... > There are still negative frequency in output file by increasing K_POINTS > and reducing tr2_ph, anyone who help me will be appreciated. Increasing the number of k-points won't help you, obviously... the first three frequencies should be zero, since they are associated to translational modes of the barycenter of the molecule. They come out non-zero for the convergence issues you mentioned in your mail. You can enforce acoustic sum rules with the appropriate flags in the input (see Doc/INPUT_PH.txt). Anyway, I don't think you need a phonon calculation to compute the energy associated to the translational motion. You should pay attention only at the other frequencies. > In addition, I intend to calculate the zero point energy of system by > PHNONS code, but it does not give the zero point energy and other > thermodynamics properties in output file. How could I do? I need your > help urgently. No comment... Cheers, GS > > Thanks in advance > Best regards > Lihui > > -- > ====================================== > Lihui Ou > PH.D Candidate in Electrochemistry > College of Chemistry and Molecular Science > Wuhan University,/430072/,Hubei Province,China > /E-mail:oulihui666 at 126.com <mailto:oulihui666 at 126.com>/ > ====================================== > > > ------------------------------------------------------------------------ > ???????????,www.yeah.net <http://www.yeah.net/?from=footer> > > > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- o ------------------------------------------------ o | Gabriele Sclauzero, PhD Student | | c/o: SISSA & CNR-INFM Democritos, | | via Beirut 2-4, 34014 Trieste (Italy) | | email: sclauzer at sissa.it | | phone: +39 040 3787 511 | | skype: gurlonotturno | o ------------------------------------------------ o
