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On 31/12/2010 5:03 AM, Marcelo Silva wrote:
<blockquote cite="mid:BLU0-SMTP1285D42C218CA05C90E1A61D4030@phx.gbl"
type="cite">
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Thank you Chris for your answer:<br>
<br>
1) The molecule has no net charge because the virtual site in the
center of mass is a point charge twice the charge in the O atom.<br>
2) Until now I've created 5 files but I don't know if I am doing
the right thing:<br>
<br>
<ul>
<li> forcefield.itp</li>
</ul>
#define _FF_OXY<br>
<br>
[ defaults ]<br>
; nbfunc comb-rule gen-pairs fudgeLJ
fudgeQQ<br>
1 2
no 1.0 1.0<br>
<br>
#include "ffnonbonded.itp"<br>
#include "ffbonded.itp"<br>
<br>
<ul>
<li> ffbonded.itp<br>
</li>
</ul>
[ bondtypes ]<br>
; i j func<br>
O O 5 (I've used function 5 because the forcefield
has a fixed length, is it right?) ;<br>
</blockquote>
<br>
If the bond length is to be fixed, then you want constraint type 1.
Bond type 5 has a different application.<br>
<br>
<blockquote cite="mid:BLU0-SMTP1285D42C218CA05C90E1A61D4030@phx.gbl"
type="cite"> <br>
<ul>
<li> ffnonbonded.itp</li>
</ul>
[ atomtypes ]<br>
; name at.num mass charge ptype
sigma epsilon<br>
O 8 15.99940 -0.123 A
3.01300e-01 4.0780822e-01<br>
COM 0 0.000000 0.246 V
0.00000e+00 0.0000000e+00<br>
<br>
<ul>
<li> atomtypes.atp<br>
</li>
</ul>
O 15.99940 ; Oxygen Atom<br>
COM 0.0 ; Virtual site (COM charge)<br>
<br>
<ul>
<li> residues.rtp<br>
</li>
</ul>
; Oxygen<br>
[ OXY ]<br>
[ atoms ]<br>
O O -0.123 1<br>
COM COM 0.246 1<br>
[ bonds ]<br>
O O<br>
<br>
3) Is it necessary more or less files? And in which file do I
specificate de virtual site?<br>
</blockquote>
<br>
Virtual site directives are listed in Table 5.6, so they need to end
up in the [moleculetype], which means they need to be in the .rtp
entry. Some of the forcefield files probably have examples of this.<br>
<br>
<blockquote cite="mid:BLU0-SMTP1285D42C218CA05C90E1A61D4030@phx.gbl"
type="cite"> 4) The virtual site in the COM is [ virtual_sites2 ]
with a = 0.5 or [ virtual_sitesn ]?<br>
</blockquote>
<br>
I guess either would work, but the former is simpler.<br>
<br>
Mark<br>
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