opls_gomc.xml

<ForceField>
    <AtomTypes>
        <Type name="CH3" class="CT" element="C" mass="12.01100" def="[C;X4](C)(H)(H)H" desc="alkane CH3" doi="10.1021/ja9621760"/>
        <Type name="CH2" class="CT" element="C" mass="12.01100" def="[C;X4](C)(C)(H)H" desc="alkane CH2" doi="10.1021/ja9621760"/>
        <Type name="CH" class="CT" element="C" mass="12.01100" def="[C;X4](C)(C)(C)H" desc="alkane CH" doi="10.1021/ja9621760"/>
        <Type name="CH4" class="CT" element="C" mass="12.01100" def="[C;X4](H)(H)(H)H" desc="alkane CH4" doi="10.1021/ja9621760"/>
        <Type name="C" class="CT" element="C" mass="12.01100" def="[C;X4](C)(C)(C)C" desc="alkane C" doi="10.1021/ja9621760"/>
        <Type name="HC" class="HC" element="H" mass="1.00800"  def="H[C;X4]" desc="alkane H" doi="10.1021/ja9621760"/>
    </AtomTypes>
    <HarmonicBondForce>
        <Bond class1="CT" class2="CT" length="0.1529" k="224262.4"/>
        <Bond class1="CT" class2="HC" length="0.109" k="284512.0"/>
    </HarmonicBondForce>
    <HarmonicAngleForce>
        <Angle class1="CT" class2="CT" class3="HC" angle="1.91113553093" k="292.88"/>
        <Angle class1="C*" class2="CT" class3="HC" angle="1.91113553093" k="292.88"/>
        <Angle class1="CT" class2="CT" class3="CT" angle="1.966986067" k="488.273"/>
         <Angle class1="HC" class2="CT" class3="HC" angle="1.88146493365" k="276.144"/>
    </HarmonicAngleForce>
    <PeriodicTorsionForce>
        <Proper class1="CT" class2="CT" class3="CT" class4="HC" periodicity1="3" phase1="0" k1="0.6276"/>
        <Proper class1="HC" class2="CT" class3="CT" class4="HC" periodicity1="3" phase1="0" k1="0.6276"/>

        <Proper class1="CT" class2="CT" class3="CT" class4="CT" periodicity1="1" phase1="0" k1="3.64"
        periodicity2="2" phase2="3.14159265359" k2="0.328"
        periodicity3="3" phase3="0" k3="0.584"/>
    </PeriodicTorsionForce>
     <NonbondedForce coulomb14scale="0.5" lj14scale="0.5">
        <Atom type="CH3" charge="-0.18" sigma="0.35" epsilon="0.276144"/>
        <Atom type="CH2" charge="-0.12" sigma="0.35" epsilon="0.276144"/>
        <Atom type="CH" charge="-0.06" sigma="0.35" epsilon="0.276144"/>
        <Atom type="CH4" charge="-0.24" sigma="0.35" epsilon="0.276144"/>
        <Atom type="C" charge="0.0" sigma="0.35" epsilon="0.276144"/>
        <Atom type="HC" charge="0.06" sigma="0.25" epsilon="0.12552"/>
    </NonbondedForce>
</ForceField>