<html>
<head>
<style>
.hmmessage P
{
margin:0px;
padding:0px
}
body.hmmessage
{
FONT-SIZE: 10pt;
FONT-FAMILY:Tahoma
}
</style>
</head>
<body class='hmmessage'>
<BR><BR>
<BLOCKQUOTE>
<HR>
From: yuhailin_79@msn.com<BR>To: pw_users@pwscf.org<BR>Subject: Help! phonon calculation at G point.<BR>Date: Wed, 17 Oct 2007 11:08:51 +0800<BR><BR>
<META content="Microsoft SafeHTML" name=Generator>
<STYLE>
.ExternalClass .EC_hmmessage P
{padding:0px;}
.ExternalClass EC_body.hmmessage
{font-size:10pt;font-family:Tahoma;}
</STYLE>
Dear all:<BR> <BR> I have some trouble with phonon calculation at G point. Recently, I have calculated two kinds of PtC, rosksalt structure and zinc-blende structure. Firstly, I have fully relaxed the lattice constants and atomic positions using quantum-espressso3.2.3. The results we attained is well agreement with these results using by VASP and CASTEP. Following, I calculate the phonon frequency at G point of the two structures. <BR>For zinc-blende structure, we attained the phonon frequency as follows:<BR> q = ( 0.000000000 0.000000000 0.000000000 )<BR> **************************************************************************<BR> omega( 1) = 1.086480 [THz] = 36.241319 [cm-1]<BR> ( 0.340996 0.000000 0.272050 0.000000 -0.549845 0.000000 )<BR> ( 0.346068 0.000000 0.276096 0.000000 -0.558022 0.000000 )<BR> omega( 2) = 1.086480 [THz] = 36.241319 [cm-1]<BR> ( -0.191604 0.000000 -0.550378 0.000000 -0.391141 0.000000 )<BR> ( -0.194454 0.000000 -0.558563 0.000000 -0.396958 0.000000 )<BR> omega( 3) = 1.086480 [THz] = 36.241319 [cm-1]<BR> ( 0.582777 0.000000 -0.340135 0.000000 0.193129 0.000000 )<BR> ( 0.591444 0.000000 -0.345194 0.000000 0.196001 0.000000 )<BR> omega( 4) = 16.225674 [THz] = 541.233828 [cm-1]<BR> ( -0.026894 0.000000 0.048005 0.000000 0.029340 0.000000 )<BR> ( 0.430439 0.000000 -0.768321 0.000000 -0.469592 0.000000 )<BR> omega( 5) = 16.225674 [THz] = 541.233828 [cm-1]<BR> ( -0.036407 0.000000 0.009944 0.000000 -0.049641 0.000000 )<BR> ( 0.582692 0.000000 -0.159157 0.000000 0.794513 0.000000 )<BR> omega( 6) = 16.225674 [THz] = 541.233828 [cm-1]<BR> ( 0.042894 0.000000 0.038539 0.000000 -0.023738 0.000000 )<BR> ( -0.686516 0.000000 -0.616817 0.000000 0.379926 0.000000 )<BR> **************************************************************************<BR>I don't know why omega(1), omega(2) and omega(3) are not equal to zero? while the optic modes is well agreement with the results attained by VASP. I want to know how to improve the accuracy. Can you tell me? Thanks a lot!<BR> <BR>For roskslt structure, we attained the phonon frequency as follows:<BR><BR> q = ( 0.000000000 0.000000000 0.000000000 )<BR> **************************************************************************<BR> omega( 1) = -16.323420 [THz] = -544.494287 [cm-1]<BR> ( 0.057067 0.000000 0.023583 0.000000 0.002155 0.000000 )<BR> ( -0.921868 0.000000 -0.380961 0.000000 -0.034805 0.000000 )<BR> omega( 2) = -16.323420 [THz] = -544.494287 [cm-1]<BR> ( -0.015312 0.000000 0.032457 0.000000 0.050295 0.000000 )<BR> ( 0.247345 0.000000 -0.524309 0.000000 -0.812467 0.000000 )<BR> omega( 3) = -16.323420 [THz] = -544.494287 [cm-1]<BR> ( 0.018065 0.000000 -0.046988 0.000000 0.035822 0.000000 )<BR> ( -0.291827 0.000000 0.759046 0.000000 -0.578678 0.000000 )<BR> omega( 4) = 0.284260 [THz] = 9.481955 [cm-1]<BR> ( 0.369808 0.000000 -0.578558 0.000000 0.160509 0.000000 )<BR> ( 0.371847 0.000000 -0.581748 0.000000 0.161394 0.000000 )<BR> omega( 5) = 0.284260 [THz] = 9.481955 [cm-1]<BR> ( 0.598650 0.000000 0.340881 0.000000 -0.150560 0.000000 )<BR> ( 0.601951 0.000000 0.342761 0.000000 -0.151390 0.000000 )<BR> omega( 6) = 0.284260 [THz] = 9.481955 [cm-1]<BR> ( -0.045937 0.000000 -0.215223 0.000000 -0.669940 0.000000 )<BR> ( -0.046191 0.000000 -0.216410 0.000000 -0.673634 0.000000 )<BR> **************************************************************************<BR>Why the phonon frequency is negative? As a test, I have caculated the elastic constants of this structure and find it satisfy formula:<BR>C44>0, C11>|C12|,C11+2C12>0. So we don't know what was wrong. Can you tell me? Thanks!<BR>The input file as shown in the follow:<BR>RS.scf.in:<BR> <BR> &control<BR> calculation='scf'<BR> restart_mode='from_scratch'<BR> tstress = .true.<BR> tprnfor = .true.<BR> prefix='RS'<BR> etot_conv_thr=1.0D-5<BR> forc_conv_thr=1.0D-4<BR> pseudo_dir = '/home/yhl/espresso-3.0/pseudo/'<BR> outdir='/home/yhl/tmp/'<BR> /<BR> &system<BR> ibrav= 2, celldm(1) =8.98, nat= 2, ntyp= 2<BR> ecutwfc =100.0<BR> ecutrho =500.0<BR> degauss =0.02<BR> smearing='mp'<BR> occupations ='smearing'<BR> /<BR> &electrons<BR> conv_thr = 1.0d-12<BR> mixing_beta = 0.7<BR> /<BR>ATOMIC_SPECIES<BR> Pt 195.08 Pt.pbe-nd-rrkjus.UPF<BR> C 12.01 C.pbe-rrkjus.UPF<BR>ATOMIC_POSITIONS<BR> Pt 0.00 0.00 0.00<BR> C 0.5 0.5 0.5<BR>K_POINTS AUTOMATIC<BR> 12 12 12 1 1 1<BR><BR>RS.ph.in<BR> <BR> phonon of PtC<BR>&inputph<BR> tr2_ph=1.0d-14,<BR> prefix='RS',<BR> ldisp=.true.,<BR> nq1=4,nq2=4,nq3=4<BR> amass(1)=195.08,<BR> amass(2)=12.01,<BR> outdir='/home/yhl/tmp/',<BR> fildyn='RS.dyn',<BR> /<BR><BR><BR>
<HR>
Discover the new Windows Vista <A href="http://search.msn.com/results.aspx?q=windows+vista&mkt=en-US&form=QBRE" target=_blank>Learn more!</A> </BLOCKQUOTE><br /><hr />Discover the new Windows Vista <a href='http://search.msn.com/results.aspx?q=windows+vista&mkt=en-US&form=QBRE' target='_new'>Learn more!</a></body>
</html>