<div>Hello gmx users. </div><div>I have tried to calculate the enthalpy of vaporization of</div><div>toluene liquid, which is about 38kJ/mol (exp. value) using </div><div>the OPLS-UA model (7 sites). I generated the toluene topology </div>
<div>adapting a template provided by PRODRG. I have obtained acceptable</div><div>value for density and structure of the liquid, but for the enthalpy </div><div>the value is much lower than expected; 18kJ/mol. </div><div>
<br></div><div>I know there are subtleties in the treatment of aromatic systems. </div><div>At Gmx users list I found some tips (see for example <a href="http://oldwww.gromacs.org/pipermail/gmx-developers/2009-January/002965.html">http://oldwww.gromacs.org/pipermail/gmx-developers/2009-January/002965.html</a> ), </div>
<div>but still I can not solve the problem.</div><div><br></div><div>I already tried numerous ways to circumvent this problem </div><div>and none worked well. It seems to me the problem may lie </div><div>in the definition of the dihedrals. </div>
<div><br></div><div>Below is the topology that I have used and the main simulation </div><div>parameters used. If someone can help me I would be very grateful. </div><div>Bests </div><div>eef</div><div><br></div><div>**** toluene.itp ****</div>
<div>[ moleculetype ]</div><div>; Name nrexcl</div><div>TOL 3</div><div><br></div><div>[ atoms ]</div><div>; nr type resnr resid atom cgnr charge mass</div><div> 1 opls_067 1 TOL CH3 1 0.000 15.0350</div>
<div> 2 opls_076 1 TOL CB 1 0.000 12.0110</div><div> 3 opls_075 1 TOL CD 1 0.000 13.0190</div><div> 4 opls_075 1 TOL CD 1 0.000 13.0190</div><div>
5 opls_075 1 TOL CD 1 0.000 13.0190</div><div> 6 opls_075 1 TOL CD 1 0.000 13.0190</div><div> 7 opls_075 1 TOL CD 1 0.000 13.0190</div><div><br>
</div><div>[ bonds ]</div><div>; ai aj fu c0, c1, ...</div><div> 1 2 1 0.153 334720.0 0.153 334720.0 ; CH3 CB</div><div> 2 3 1 0.141 418400.0 0.141 418400.0 ; CB CD</div><div>
2 7 1 0.141 418400.0 0.141 418400.0 ; CB CD</div><div> 3 4 1 0.141 418400.0 0.141 418400.0 ; CD CD</div><div> 4 5 1 0.141 418400.0 0.141 418400.0 ; CD CD</div>
<div> 5 6 1 0.141 418400.0 0.141 418400.0 ; CD CD</div><div> 6 7 1 0.141 418400.0 0.141 418400.0 ; CD CD</div><div><br></div><div>[ angles ]</div><div>; ai aj ak fu c0, c1, ...</div>
<div> 1 2 3 1 120.0 418.4 120.0 418.4 ; CH3 CB CD </div><div> 1 2 7 1 120.0 418.4 120.0 418.4 ; CH3 CB CD </div><div> 3 2 7 1 120.0 418.4 120.0 418.4 ; CD CB CD </div>
<div> 2 3 4 1 120.0 418.4 120.0 418.4 ; CB CD CD </div><div> 3 4 5 1 120.0 418.4 120.0 418.4 ; CD CD CD </div><div> 4 5 6 1 120.0 418.4 120.0 418.4 ; CD CD CD </div>
<div> 5 6 7 1 120.0 418.4 120.0 418.4 ; CD CD CD </div><div> 2 7 6 1 120.0 418.4 120.0 418.4 ; CB CD CD </div><div><br></div><div><br></div><div>[ dihedrals ]</div>
<div>; ai aj ak al fu c0, c1, m, ...</div><div> 2 7 3 1 2 0.0 1673.6 ; imp CB CD CD CH3 </div><div> 2 3 4 5 1 180.0 12.9704 2 ; imp CB CD CD CD </div>
<div> 3 4 5 6 1 180.0 12.9704 2 ; imp CD CD CD CD </div><div> 4 5 6 7 1 180.0 12.9704 2 ; imp CD CD CD CD </div><div> 5 6 7 2 1 180.0 12.9704 2 ; imp CD CD CD CB </div>
<div> 6 7 2 3 1 180.0 12.9704 2 ; imp CD CD CB CD </div><div> 7 2 3 4 1 180.0 12.9704 2 ; imp CD CB CD CD </div><div><br></div><div><br></div><div>**** toluene.mdp ****</div>
<div>integrator = md </div><div>nstlist = 5</div><div>ns_type = grid</div><div>pbc = xyz</div><div>rlist = 1.2</div><div>domain-decomposition = no</div>
<div>coulombtype = Cut-off</div><div>rcoulomb-switch = 0</div><div>rcoulomb = 1.2</div><div>vdw-type = Cut-off</div><div>rvdw-switch = 0</div><div>rvdw = 1.2</div>
<div>DispCorr = EnerPres</div><div>table-extension = 1</div><div>energygrp_table = </div><div>fourierspacing = 0.12</div><div>Tcoupl = berendsen</div><div>tc-grps = System</div>
<div>tau_t = 0.1</div><div>ref_t = 300</div><div>Pcoupl = No</div><div>Pcoupltype = isotropic</div><div>tau_p = 1</div><div>compressibility = 5.0e-5</div>
<div>ref_p = 1.1</div><div>constraints = none</div><div>constraint-algorithm = Lincs</div><div>unconstrained-start = no</div><div>energygrp_excl = </div><div><br></div><div>
**** toluene.gro ****</div><div><div> PRODRG COORDS</div><div> 7</div><div> 1TOL CH3 1 0.159 -0.143 -0.050</div><div> 1TOL CB 2 0.154 -0.227 0.078</div><div> 1TOL CD 3 0.224 -0.349 0.084</div>
<div> 1TOL CD 4 0.219 -0.426 0.203</div><div> 1TOL CD 5 0.145 -0.379 0.313</div><div> 1TOL CD 6 0.075 -0.256 0.308</div><div> 1TOL CD 7 0.080 -0.180 0.189</div><div>
0.51300 0.51300 0.51300</div><div><br></div><div><br></div><div><br></div></div>_______________________________________<br>Eudes Eterno Fileti<br>Centro de Ciências Naturais e Humanas<br>Universidade Federal do ABC — CCNH<br>
Av. dos Estados, 5001<br>Santo André - SP - Brasil<br>CEP 09210-971<br>+55.11.4437-0196<br><a href="http://fileti.ufabc.edu.br">http://fileti.ufabc.edu.br</a><br>