<ForceField>
 <AtomTypes>
  <Type name="1" class="C_CO2" element="C" mass="12.01060"/>
  <Type name="2" class="O_CO2" element="O" mass="15.99943"/>
  <Type name="4" class="M" element="H" mass="1.0"/>
 </AtomTypes>
 <Residues>
  <Residue name="co2">
    Atom names should match those in .pdb file
   <Atom name="C" type="1"/>
   <Atom name="O1" type="2"/> 
   <Atom name="O2" type="2"/>

   <Bond from="0" to="1"/>
   <Bond from="0" to="2"/>

  </Residue>
 </Residues>

  <HarmonicBondForce>
    <Bond class1="C_CO2" class2="O_CO2" length="0.1163" k="8.443e5"/>
  </HarmonicBondForce>

  <HarmonicAngleForce>
    <Angle class1="O_CO2" class2="C_CO2" class3="O_CO2" angle="3.14159" k="451.9"/>
  </HarmonicAngleForce>


 <AmoebaMultipoleForce  direct11Scale="1.0"  direct12Scale="1.0"  direct13Scale="1.0"  direct14Scale="1.0"  mpole12Scale="0.5"  mpole13Scale="0.5"  mpole14Scale="0.8"  mpole15Scale="0.8"  mutual11Scale="0.0"  mutual12Scale="0.0"  mutual13Scale="1.0"  mutual14Scale="1.0"  polar12Scale="1.0"  polar13Scale="0.0"  polar14Intra="0.5"  polar14Scale="1.0"  polar15Scale="1.0"  >
     <Multipole type="1" kz="2" kx="0" c0="0.884358" d1="0" d2="0" d3="2.64589e-07" q11="6.41139e-05" q21="0" q22="6.41139e-05" q31="0" q32="0" q33="-0.000128228" />
     <Multipole type="2" kz="1" kx="0" c0="-0.442179" d1="0" d2="0" d3="-0.00621566" q11="-3.68839e-05" q21="0" q22="-3.68839e-05" q31="0" q32="0" q33="7.37679e-05" />
     <Multipole type="4" kz="0" kx="0" c0="0.0" d1="0" d2="0" d3="0" q11="0" q21="0" q22="0" q31="0" q32="0" q33="0" />


    <Polarize type="1" polarizability="1.333661e-04" thole="0.33" pgrp1="2" pgrp2="3" />
    <Polarize type="2" polarizability="1.227116e-03" thole="0.33" pgrp1="1" />
    <Polarize type="4" polarizability="1e-9" thole="0.33" pgrp1="1" />
    <!--
    -->
</AmoebaMultipoleForce>

 <CustomNonbondedForce bondCutoff="4"
    energy="A*K2*exBr - Adi*(f6*C6/(r^6) - f8*C8/(r^8) - f10*C10/(r^10) - f12*C12/(r^12));
    A=Aex-Ael-Ain-Adh;
    Aex=(Aexch1*Aexch2);
    Ael=(Aelec1*Aelec2);
    Ain=(Aind1*Aind2);
    Adh=(Adhf1*Adhf2);
    Adi=(Adisp1*Adisp2);
    K2=(Br^2)/3 + Br + 1;
    f12 = f10 - exX*( (1/39916800)*(X^11)*(1 + X/12) );
    f10 = f8 - exX*( (1/362880)*(X^9)*(1 + X/10 ) );
    f8 = f6 - exX*( (1/5040)*(X^7)*(1 + X/8 ) );
    f6 = 1 - exX*(1 + X * (1 + (1/2)*X*(1 + (1/3)*X*(1 + (1/4)*X*(1 + (1/5)*X*(1 + (1/6)*X ) ) )  ) ) );
    exX = exp(-X);
    X = Br - r * ( 2*(B^2)*r + 3*B )/(Br^2 + 3*Br + 3) ;
    exBr = exp(-Br);
    Br = B*r;
    B=sqrt(Bexp1*Bexp2);
    C6=sqrt(C61*C62); C8=sqrt(C81*C82); C10=sqrt(C101*C102); C12=sqrt(C121*C122)"
    >
    <PerParticleParameter name="Aexch"/>
    <PerParticleParameter name="Aelec"/>
    <PerParticleParameter name="Aind"/>
    <PerParticleParameter name="Adhf"/>
    <PerParticleParameter name="Adisp"/>
    <PerParticleParameter name="Bexp"/>
    <PerParticleParameter name="C6"/>
    <PerParticleParameter name="C8"/>
    <PerParticleParameter name="C10"/>
    <PerParticleParameter name="C12"/>

    <Atom class="C_CO2" Aexch="7.073403e+01" Aelec="3.871424e+01" Aind="3.020657e+01" Adhf="4.204415e+00" Adisp="7.114610e-01" Bexp="3.820882e+01" C6="1.262157e-03" C8="6.962318e-05" C10="3.262527e-06" C12="2.019001e-07"/>
    <Atom class="O_CO2" Aexch="2.215524e+02" Aelec="1.257688e+02" Aind="1.276994e+01" Adhf="5.232102e+01" Adisp="1.072543e+00" Bexp="4.621758e+01" C6="9.540046e-04" C8="4.693183e-05" C10="3.163703e-06" C12="1.458385e-07"/>

 </CustomNonbondedForce>


 <!--
<CustomManyParticleForce particlesPerSet="3" permutationMode="SinglePermutation"
    bondCutoff="4" energy=
    "C9*(1+3*cos(theta1)*cos(theta2)*cos(theta3))/(r12*r13*r23)^3;
      ;
      C9=scalec9*(v1*v2*v3)^(1/3);
      ;
      theta1=angle(p1,p2,p3); 
      theta2=angle(p2,p3,p1); 
      theta3=angle(p3,p1,p2);
      r12=distance(p1,p2); 
      r13=distance(p1,p3); 
      r23=distance(p2,p3);">

      <TypeFilter index="0" types="1,2"/>
      <TypeFilter index="1" types="1,2"/>
      <TypeFilter index="2" types="1,2"/>

     <GlobalParameter name="scalec9" defaultValue="1.13"/>
     <PerParticleParameter name="v"/>
     <Atom class="M" v="0.0" filterType="3" />
     <Atom class="C_CO2"  v="3.41728E-09" filterType="1"/>
     <Atom class="O_CO2" v="1.78553E-06" filterType="1"/>

     A few notes:
     1. This force field is the ATM 3-body dispersion force, with functional form as given in \cite{Oakley2009a}
     2. The dispersion is scaled to reproduce the isotropic c9 coefficient given by CCSD
 </CustomManyParticleForce>
 -->



</ForceField>

