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<BODY bgColor=#eaeaea>Dear Prof. BaroniŁ¬
<DIV> </DIV>
<DIV>ˇˇThanks for your prompt reply.</DIV>
<DIV> </DIV>
<DIV>(1) The four-layer slab</DIV>
<DIV> I did get warnings about the setup of the four-layer
slab in the output file:</DIV>
<DIV> warning: symmetry operation # 4 not
allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR> warning:
symmetry operation # 11 not allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR> warning:
symmetry operation # 12 not allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR> warning:
symmetry operation # 13 not allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR> warning:
symmetry operation # 19 not allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR> warning:
symmetry operation # 20 not allowed. fractional
translation:<BR> 0.3333333 -0.3333333
0.0000000 in crystal coordinates<BR></DIV>
<DIV> The real-space FFT grids in this calculation were:</DIV>
<DIV> G cutoff = 146.8225 ( 47267
G-vectors) FFT grid: ( 25,
25,180)<BR> G cutoff = 73.4112 (
16847 G-vectors) smooth grid: ( 18, 18,125)<BR></DIV>
<DIV>(2) The six-layer slab </DIV>
<DIV> Then I performed a calculation of a six-layer slab. The
initial positions were:</DIV>
<DIV> Cu
0.5000000 0.2886751
-1.632993<BR> Cu
0.0000000 0.5773505
-0.816497<BR> Cu
0.0000000 0.0000000
0.000000<BR> Cu
0.5000000 0.2886751
0.816497<BR> Cu
0.0000000 0.5773503
1.632993<BR> Cu
0.0000000 0.0000000
2.449490</DIV>
<DIV> </DIV>
<DIV> After relaxation, the final positions are:</DIV>
<DIV> Cu
0.500000000 0.288675100
-1.626940097<BR> Cu
0.000000000 0.577350500
-0.819973440<BR> Cu
0.000000000 0.000000000
-0.003573650<BR> Cu
0.500000000 0.288675100
0.818345337<BR> Cu
0.000000000 0.577350300
1.634784508<BR> Cu
0.000000000 0.000000000 2.446847342<BR></DIV>
<DIV> The interlayer spacings on the two sides of the slab are
0.812062834 and 0.806966657, respectively. This time the asymmetry becomes
larger than the case of four-layer slab. </DIV>
<DIV> </DIV>
<DIV> I noticed that in the output file there are warnings as below:</DIV>
<DIV> warning: symmetry operation # 4 not
allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates<BR> warning:
symmetry operation # 11 not allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates<BR> warning:
symmetry operation # 12 not allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates<BR> warning:
symmetry operation # 13 not allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates<BR> warning:
symmetry operation # 19 not allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates<BR> warning:
symmetry operation # 20 not allowed. fractional
translation:<BR> 0.3333334 -0.3333333
-0.0909088 in crystal coordinates</DIV>
<DIV>
<DIV> And the FFT grids are: </DIV>
<DIV> G cutoff = 146.8225 ( 57757
G-vectors) FFT grid: ( 25,
25,225)<BR> G cutoff = 73.4112 (
20595 G-vectors) smooth grid: ( 18, 18,160)</DIV>
<DIV><BR> Since I have six atom layers and six vacuume layers, it seems
that the code translated the FFT grids along the z direction about eleventh of
the z-axis length to judge whether the grid (nr3) can
coincide with itself. It failed due to 225 can't be divided by 11. I
have tried to set "nr1=25, nr2=25, nr3 =220" manually (also nr3=231
and 242), but these FFT grids were not allowed. </DIV>
<DIV> A solution to this may be to change the FFT library which
allows factor of 11, and recompile the PWSCF code. Another
solution to this problem may be to reduce or increase the vacuum layers so
that the FFT grids are appropriate for the symmetric operations. But since
I want to see the dependence of relaxations of surface layers on the
slab thickness, I have to fix the vacuum thickness for different slabs. Is there
anyway to get symmetric relaxations of different even-layer slabs? For example,
is it possible to shift the FFT grid at the setup so that it coincides
with symmetry of different slabs?</DIV></DIV>
<DIV> </DIV>
<DIV>Best regards,</DIV>
<DIV>Lucky </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=2>
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<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">Dear
Lucky:
<DIV><BR class=khtml-block-placeholder></DIV>
<DIV>the non-symmetric part of the relaxation is very small and possibly
not very meaningful. Nevertheless, I agree that if reflection were an
exact symmetry of your system, this asymmetry should vanish. One
possible explanation could be that reflection symmetry is (slightly)
violated by your numerical setup, e.g. the real-space fft grid could be
not symmetryc.?/DIV>
<DIV><BR class=khtml-block-placeholder></DIV>
<DIV>Stefano</DIV>
<DIV><BR>
<DIV>
<DIV>On Oct 11, 2006, at 3:14 AM, lucky8121 wrote:</DIV><BR
class=Apple-interchange-newline>
<BLOCKQUOTE type="cite">
<DIV style="MARGIN: 0px">Dear users,</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">I am a new user of PWSCF. I am doing the
structure relaxation of metal slabs.</DIV>
<DIV style="MARGIN: 0px">The relaxations (interlayer spacings) on the
two sides of the odd-layer slab are symmetric. However, I met problem
with the relaxation of even-layer slabs.</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">The initial positions of the Cu(111) slab
were:</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.577350269190<SPAN
class=Apple-converted-space>?</SPAN>-1.224744871392</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.000000000000<SPAN
class=Apple-converted-space>?</SPAN>-0.408248290464</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.500000000 <SPAN
class=Apple-converted-space>?</SPAN>0.288675134595 <SPAN
class=Apple-converted-space>?</SPAN>0.408248290464</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.577350269190 <SPAN
class=Apple-converted-space>?</SPAN>1.224744871392</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">After relaxation (forc_conv_thr = 4.0D-4),
the final positions are:</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.577350269<SPAN
class=Apple-converted-space>?</SPAN>-1.207031882</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.000000000<SPAN
class=Apple-converted-space>?</SPAN>-0.404842681</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.500000000 <SPAN
class=Apple-converted-space>?</SPAN>0.288675135 <SPAN
class=Apple-converted-space>?</SPAN>0.404671325</DIV>
<DIV style="MARGIN: 0px">Cu <SPAN
class=Apple-converted-space>???</SPAN>0.000000000 <SPAN
class=Apple-converted-space>?</SPAN>0.577350269 <SPAN
class=Apple-converted-space>?</SPAN>1.207203237</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">As you can see, the relaxations on the two
sides of the slab are different. The same case occured whether I set
"nosym" as ".true." or ".false.". This is strange. I wonder whether
someone else has met the same problem and how he or she solved it.
Thanks.</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">By the way, I have used a vacuum of 12.7
angstrom.</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">Best regards</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MARGIN: 0px">lucky</DIV>
<DIV style="MARGIN: 0px"><A
href="mailto:lucky8121@sohu.com">lucky8121@sohu.com</A></DIV>
<DIV style="MARGIN: 0px">2006-10-11</DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px"><BR></DIV>
<DIV
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<DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span
style="FONT-SIZE: 12px">---</SPAN></SPAN></SPAN></FONT></DIV>
<DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px">Stefano Baroni -
SISSA</SPAN></SPAN></SPAN></FONT><FONT class=Apple-style-span
size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span
style="FONT-SIZE: 12px">?</SPAN></SPAN></SPAN></FONT><FONT
class=Apple-style-span size=3><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px">&</SPAN></SPAN></SPAN></FONT><FONT
class=Apple-style-span size=3><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px">?</SPAN></SPAN></SPAN></FONT><FONT
class=Apple-style-span size=3><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px">DEMOCRITOS National Simulation Center -
Trieste</SPAN></SPAN></SPAN></FONT></DIV>
<DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px">[+39] 040 3787 406 (tel)
-528 (fax) / stefanobaroni (skype)</SPAN></SPAN></SPAN></FONT></DIV>
<DIV style="MIN-HEIGHT: 14px; MARGIN: 0px; FONT: 12px Helvetica"><BR
style="FONT-SIZE: 12px"></DIV>
<DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px">Please, if possible,
don't</SPAN></SPAN></SPAN></FONT><FONT class=Apple-style-span
size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span
style="FONT-SIZE: 12px">?</SPAN></SPAN></SPAN></FONT><FONT
class=Apple-style-span size=3><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px"><SPAN class=Apple-style-span
style="FONT-SIZE: 12px">send me MS Word or PowerPoint
attachments</SPAN></SPAN></SPAN></FONT></DIV>
<DIV style="MARGIN: 0px"><FONT class=Apple-style-span size=3><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px">Why?
See:</SPAN></SPAN></SPAN></FONT><FONT class=Apple-style-span
size=3><SPAN class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
class=Apple-style-span style="FONT-SIZE: 12px"><SPAN
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class=Apple-style-span
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