<DIV>
<DIV>Dear all,</DIV>
<DIV> 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 possible reseaons: <BR> (1) wrong data file read.<BR> (2) wrong atomic masses given in input will yield wrong frequencies (but<BR>the content of file fildyn should be valid, since the force constants, not<BR>the dynamical matrix, are written to file).<BR> (3) convergence threshold for either SCF (conv thr) or phonon calculation<BR>(tr2 ph) too large: try to reduce them.<BR> (4) maybe your system does have negative or strange phonon frequencies,<BR>with the approximations you used. A negative frequency signals a<BR>mechanical instability of the chosen structure. Check that the structure<BR>is reasonable, and check the following parameters:<BR> – The cutoff for wavefunctions, ecutwfc<BR> – For US PP: the cutoff for the charge density, ecutrho<BR> – The k-point grid, especially for metallic systems!<BR></DIV>
<DIV>My calculated process as follows: </DIV>
<DIV>(1) Optimizing CO2 structure(input file as follows);</DIV>
<DIV> &CONTROL<BR> calculation = 'relax' ,<BR> restart_mode = 'from_scratch' ,<BR> outdir = '/home/olh/tmp/' ,<BR> pseudo_dir = '/home/olh/pseudo/' ,<BR> prefix = 'CO2' ,<BR> /<BR> &SYSTEM<BR> ibrav = 1,<BR> celldm(1) = 15.11781502,<BR> nat = 3,<BR> ntyp = 2,<BR> ecutwfc = 26 ,<BR> ecutrho = 260 ,<BR> occupations = 'smearing' ,<BR> degauss = 0.02 ,<BR> smearing = 'methfessel-paxton' ,<BR> nspin = 2 ,<BR> starting_magnetization(1) = 0.5,<BR> starting_magnetization(2) = 0.5,<BR> /<BR> &ELECTRONS<BR> conv_thr = 1.D-12 ,</DIV>
<DIV> mixing_beta = 0.4D0 ,<BR> /<BR> &IONS<BR> ion_dynamics = 'bfgs' ,<BR> /<BR>ATOMIC_SPECIES<BR> C 12.01100 C.pbe-rrkjus.UPF<BR> O 15.99940 O.pbe-rrkjus.UPF<BR>ATOMIC_POSITIONS angstrom<BR> C 4.000000000 4.000000000 4.000000000 1 1 1<BR> O 5.160000000 4.000000000 4.000000000 1 1 1<BR> O 2.840000000 4.000000000 4.000000000 1 1 1<BR>K_POINTS gamma</DIV>
<DIV> </DIV>
<DIV>(2) Performing scf calculations:</DIV>
<DIV> &CONTROL<BR> calculation = 'scf' ,<BR> restart_mode = 'from_scratch' ,<BR> outdir = '/home/olh/tmp/' ,<BR> pseudo_dir = '/home/olh/pseudo/' ,<BR> prefix = 'CO2' ,<BR> /<BR> &SYSTEM<BR> ibrav = 1,<BR> celldm(1) = 15.11781502,<BR> nat = 3,<BR> ntyp = 2,<BR> ecutwfc = 26 ,<BR> ecutrho = 260 ,<BR> occupations = 'smearing' ,<BR> degauss = 0.02 ,<BR> smearing = 'methfessel-paxton' ,<BR> nspin = 2 ,<BR> starting_magnetization(1) = 0.5,<BR> starting_magnetization(2) = 0.5,<BR> /<BR> &ELECTRONS<BR> conv_thr = 1.D-12 ,</DIV>
<DIV> mixing_beta = 0.4D0 ,<BR> /<BR>ATOMIC_SPECIES<BR> C 12.01100 C.pbe-rrkjus.UPF<BR> O 15.99940 O.pbe-rrkjus.UPF<BR>ATOMIC_POSITIONS angstrom<BR> C 4.000000000 4.000000000 4.000000000 0 0 0<BR> O 5.172018724 4.000000000 4.000000000 0 0 0<BR> O 2.827981276 4.000000000 4.000000000 0 0 0<BR>K_POINTS automatic<BR> 16 16 16 1 1 1</DIV>
<DIV> </DIV>
<DIV>(3) Performing frequency calculation using PHONOS codes:</DIV>
<DIV>phonons of CO2 at Gamma<BR> &inputph<BR> tr2_ph=1.0d-20,<BR> prefix='CO2',<BR> epsil=.false.,<BR> amass(1)=12.0110,<BR> amass(2)=15.9994,<BR> outdir='/home/olh/tmp/',<BR> fildyn='CO2.dynG',<BR> /<BR>0.0 0.0 0.0</DIV>
<DIV> </DIV>
<DIV>Finally, I obtained the frequency of CO2 molecule, output file as follows:</DIV>
<DIV> Convergence has been achieved</DIV>
<DIV> Number of q in the star = 1<BR> List of q in the star:<BR> 1 0.000000000 0.000000000 0.000000000</DIV>
<DIV> Diagonalizing the dynamical matrix</DIV>
<DIV> q = ( 0.000000000 0.000000000 0.000000000 )</DIV>
<DIV>**************************************************************************<BR> omega( 1) = -3.661345 [THz] = -122.130124 [cm-1]<BR> omega( 2) = -3.661345 [THz] = -122.130124 [cm-1]<BR> omega( 3) = 3.659957 [THz] = 122.083850 [cm-1]<BR> omega( 4) = 7.879986 [THz] = 262.849774 [cm-1]<BR> omega( 5) = 7.879986 [THz] = 262.849774 [cm-1]<BR> omega( 6) = 19.746862 [THz] = 658.688787 [cm-1]<BR> omega( 7) = 19.746862 [THz] = 658.688787 [cm-1]<BR> omega( 8) = 38.945041 [THz] = 1299.075383 [cm-1]<BR> omega( 9) = 70.000609 [THz] = 2334.984491 [cm-1]<BR>**************************************************************************<BR> Mode symmetry, D_4h(4/mmm) point group:</DIV>
<DIV> omega( 1 - 2) = -122.1 [cm-1] --> E_g X_5 M_5 R<BR> omega( 3 - 3) = 122.1 [cm-1] --> A_2u X_4' M_4' I<BR> omega( 4 - 5) = 262.8 [cm-1] --> E_u X_5' M_5' I<BR> omega( 6 - 7) = 658.7 [cm-1] --> E_u X_5' M_5' I<BR> omega( 8 - 8) = 1299.1 [cm-1] --> A_1g X_1 M_1 R<BR> omega( 9 - 9) = 2335.0 [cm-1] --> A_2u X_4' M_4' I</DIV>
<DIV> **************************************************************************</DIV>
<DIV> PHONON : 1h48m CPU time, 2h25m wall time<BR>......</DIV>
<DIV>There are still negative frequency in output file by increasing K_POINTS and reducing tr2_ph, anyone who help me will be appreciated. </DIV>
<DIV>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.</DIV>
<DIV> </DIV>
<DIV>Thanks in advance </DIV>
<DIV>Best regards </DIV>
<DIV>Lihui </DIV><BR>--<BR></DIV>
<DIV>
<DIV>
<DIV><FONT face="Arial" size="3">======================================</FONT></DIV>
<DIV><FONT face="Arial" size="3">Lihui Ou</FONT></DIV>
<DIV><FONT face="Arial" size="3">PH.D Candidate in Electrochemistry </FONT></DIV>
<DIV><FONT face="Arial" size="3">College of Chemistry and Molecular Science </FONT></DIV>
<DIV><FONT face="Arial" size="3">Wuhan University,<EM>430072</EM>,Hubei Province,China </FONT></DIV>
<DIV><EM><FONT face="Arial" size="3">E-mail:</FONT><A href="mailto:oulihui666@126.com" target="_blank"><FONT face="Arial" size="3">oulihui666@126.com</FONT></A></EM></DIV>
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