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I am trying to get the parameters right for a solvent molecule.<br><br>
Appear to have the partial charges right, the dipole moment is within
0.25 % (2.27 vs 2.276). Started with similar functional groups in
the forcefield (G96 43a2x) and made some minor adjustments to get that
close.<br><br>
Managed to get the density pretty good too, within 0.14 % (1035 vs
1036). Adjusted the value of L-J parameter V (Cij(6)) slightly to
get this right.<br><br>
Problem is that the heat of vaporisation appears to be a long way off
(-12.2 vs 58.0). To calculate this (I think this is correct ....),
I took the internal energy from g_energy (26,545), divided by the number
of molecules (1,800) to give 14.7 kJ/mol for the internal energy.
Then subtracted this value from RT (2.47 kJ/mol), DHvap =
-12.2.<br><br>
To get the correct value of DHvap the internal energy needs to be in the
order of - 55 kJ/mol. This seems to be a large difference.
Either I have calculated something incorrectly, are using the incorrect
method, or the parameters are very wrong.<br><br>
If the former, then where did I go wrong?<br><br>
If the latter, then I guess I need to change V and W for the L-J
potential such that the shape of the potential is similar (should
preserve the density?) but the minimum energy is a fair amount larger (to
decrease the value of 1-4 LJ and LJ SR enough)?<br><br>
Thank you for any comments.<br><br>
Catch ya,<br>
<x-sigsep><p></x-sigsep>
<b>Dr. Dallas Warren<br>
</b><i>Research Fellow<br>
</i>Department of Pharmaceutical Biology and Pharmacology<br>
Victorian College of Pharmacy, Monash University<br>
381 Royal Parade, Parkville VIC 3010<br>
<font color="#0000FF"><u>dallas.warren@vcp.monash.edu.au<br>
</u></font>+61 3 9903 9083<br>
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