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<TITLE>Re: [CPMD-list] forces, convergence and gga</TITLE>
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<DIV id=idOWAReplyText52756 dir=ltr>
<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Hi,</FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=Arial size=2>Thanks for the replies (Axel
also).</FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=Arial size=2>Referring to question 2: </FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2>Maybe i didn't formulate the problem as it
should. What i did is the following:<BR>I want to use the VDB uspp and BLYP
functional (because B3LYP describes the molecule relatively good in
gaussian). So i tried different cutoff values (20 to 45) and looked for
convergence for some 'important' bond lengths. I think
the convergence for S-N and S-C is not really good, but C=C and C-H seem to
converge nicely (cutoff values going from 20 Ry to 45 Ry).</FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2></FONT><FONT face=Arial
size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=Arial size=2>Values for S-N going from 20 to 45 Ry
(steps of 5 Ry) in Angstrom:</FONT><FONT face=Arial size=2></DIV>
<TABLE style="WIDTH: 288pt; BORDER-COLLAPSE: collapse" cellSpacing=0
cellPadding=0 width=384 border=0 x:str>
<COLGROUP>
<COL style="WIDTH: 48pt" span=6 width=64>
<TR style="HEIGHT: 12.75pt" height=17>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent"
width=64 height=17 x:num="1.72176"><FONT size=2>1.72176</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.7177199999999999"><FONT size=2>1.71772</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.7183600000000001"><FONT size=2>1.71836</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.71851"><FONT size=2>1.71851</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.71658"><FONT size=2>1.71658</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.7177199999999999"><FONT
size=2>1.71772</FONT></TD></TR></TABLE>
<DIV dir=ltr>Values for C-N:</DIV>
<DIV dir=ltr>
<TABLE style="WIDTH: 288pt; BORDER-COLLAPSE: collapse" cellSpacing=0
cellPadding=0 width=384 border=0 x:str>
<COLGROUP>
<COL style="WIDTH: 48pt" span=6 width=64>
<TR style="HEIGHT: 12.75pt" height=17>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent"
width=64 height=17 x:num="1.8136699999999999"><FONT
size=2>1.81367</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.8200099999999999"><FONT size=2>1.82001</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.81453"><FONT size=2>1.81453</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num><FONT size=2>1.82000</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.8188800000000001"><FONT size=2>1.81888</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.82267"><FONT
size=2>1.82267</FONT></TD></TR></TABLE></DIV>
<DIV dir=ltr>Values for C=C:</DIV>
<DIV dir=ltr>
<TABLE style="WIDTH: 288pt; BORDER-COLLAPSE: collapse" cellSpacing=0
cellPadding=0 width=384 border=0 x:str>
<COLGROUP>
<COL style="WIDTH: 48pt" span=6 width=64>
<TR style="HEIGHT: 12.75pt" height=17>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent"
width=64 height=17 x:num="1.429"><FONT size=2>1.42900</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.41553"><FONT size=2>1.41553</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.4152100000000001"><FONT size=2>1.41521</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.41571"><FONT size=2>1.41571</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.4153199999999999"><FONT size=2>1.41532</FONT></TD>
<TD class=xl24
style="BORDER-RIGHT: #d4d0c8; BORDER-TOP: #d4d0c8; BORDER-LEFT: #d4d0c8; WIDTH: 48pt; BORDER-BOTTOM: #d4d0c8; BACKGROUND-COLOR: transparent"
width=64 x:num="1.41554"><FONT
size=2>1.41554</FONT></TD></TR></TABLE></DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>The question now is either or not the S-N and C-N values may be
considered as converged or not? And maybe someone knows why the S-N and C-N
values are not as good converged as the C=C and C-H values. We do know from
experience that C-N and S-N (in our molecule) are difficult to
converge in gaussian calculations also, so maybe it's just an functional issue,
but maybe i'm just doing something wrong with cpmd..</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>With kind regards,</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Christopher<BR>Undergrad. Student</DIV>
<DIV dir=ltr>University of Antwerp</DIV>
<DIV dir=ltr> </DIV></FONT>
<DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV><FONT face=Arial
size=2></FONT></DIV>
<DIV dir=ltr>
<DIV dir=ltr><BR></DIV>
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</DIV>
<DIV dir=ltr><FONT face=Tahoma size=2><B>From:</B> Juerg Hutter
[mailto:hutter@pci.unizh.ch]<BR><B>Sent:</B> Mon 5/12/2005 11:25<BR><B>To:</B>
De Dobbelaere Christopher<BR><B>Cc:</B> cpmd-list@cpmd.org<BR><B>Subject:</B>
Re: [CPMD-list] forces, convergence and gga<BR></FONT><BR></DIV></DIV>
<DIV>
<P><FONT size=2>Hi<BR>> I've got 3 little questions..<BR>><BR>> 1) I'm
doing a md run of a molecule surrounded by water molecules. In order to check if
the forces acting on the molecules are not too large, i'd like to check out the
forces acting on them (since i didn't do a geometry optimalization at the
beginning). I checked out the manual and found that it is possible to print the
acting forces during the trajectory in the TRAJECTORY file. Since the md run is
'finished' it seems to be a little late for that..<BR>> But now I was
wondering what the initial forces acting on the atoms would be. Since they are
listed in the output file that seemed not to be a problem. But what are the
units of the forces? They are not mentioned in the manual, so i suppose it's
a.u.? If it it, what's the conversion to convert them to dyne, Newton,.. or
something else?<BR><BR>Forces are in a.u., I'm sorry but I'm too lazy to do the
work for<BR>converting into other units for you.<BR><BR>BTW. You can calculate
the forces on the atoms from the trajectory file<BR>using positions and
velocities by inverting the velocity Verlet<BR>algorithm.<BR><BR>><BR>> 2)
Before I did a md run, i checked out some dft functionals to describe the
geometry of the molecule. I got convergence for C=C, C-H, more or less
convergence for S-N but the C-S bound seems not to convergence at all (the
C's from a aromatic system and C is attached to it). Does anyone have an idea
why that could be?<BR>><BR>What do you mean by convergence? All functionals
give the same values?<BR>As there is no series of functionals that will give
better and better<BR>results you cannot talk about convergence in this
case.<BR><BR>It might be a good idea to get a "correct" value for the
problematic<BR>bond (e.g. by a large basis set CCSD(T) calculation) and then
look for<BR>the functional that comes close to that value.<BR><BR><BR>> 3) In
the manual, the GGA functional is mentioned. But what's the exact functional
behind that GGA implemented in cpmd? Since GGA stands for
Generalized-gradient-approximation, it doesnt give me any new
information..<BR>><BR><BR>The reference to the papers is usually written in
the output for all<BR>functionals. You can also have a look into the file
"functionals.F".<BR><BR>regards<BR><BR>Juerg Hutter<BR><BR><BR><BR>> Thanks
in advance!<BR>><BR>><BR>><BR>> Christopher<BR>> Undergrad.
Student<BR>> University of
Antwerp<BR>><BR>><BR>><BR></FONT></P></DIV>
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