* * Parameter File for NERD (Nath, Escobedo, and Pablo) United Atom Force Field * * Parameters From: * * "On the simulation of vapor-liquid equilibria for alkanes" * Shyamal K. Nath, Fernando A. Escobedo and Juan J. de Pablo, * J. Chem. Phys., 1998, 108(23)(15 Jun), p9905-9911 * DOI: 10.1063/1.476429 * * "Simulation of vapour-liquid equilibria for branched alkanes" * Shyamal K. Nath and Juan J. Pablo, Mol. Phys., 2000, 98(4) p231-238 * DOI: 10.1080/00268970009483286 * * and * * "New forcefield parameters for branched hydrocarbons" * Shyamal K. Nath and Rajesh Khare, J. Chem. Phys., 2001, 115(23), p10837-10844 * DOI: 10.1063/1.1418731 BONDS ! !V(bond) = Kb(b - b0)**2 ! !Kb: kcal/mole/A**2 !b0: A ! ! Kb (kcal/mol) = Kb (K) * Boltz. const.; (9999999999 if no stretching) ! !atom type Kb b0 description CA3 CH2 9999999999 1.540 ! (ex. n-butane) CB3 CB3 9999999999 1.540 ! (ethane only) CC3 CH2 9999999999 1.540 ! (propane only) CD3 CH1 9999999999 1.540 ! (isobutane only) CE3 CH2 9999999999 1.540 ! (2-methylbutane only) CE3 CH1 9999999999 1.540 ! (2-methylbutane only) CG3 CT 9999999999 1.540 ! (2,2-dimethylpropane only) CJ3 CT 9999999999 1.540 ! (2,2-dimethylbutane only) CK3 CH1 9999999999 1.540 ! (ex. 2-methylpentane) CK3 CT 9999999999 1.540 ! (ex. 2,2-dimethylpentane) CM3 CH2 9999999999 1.540 ! (ex. 2,2-dimethylbutane) CH2 CH2 9999999999 1.540 ! (ex. n-butane) CH2 CH1 9999999999 1.540 ! (ex. 2-methylbutane) CH2 CT 9999999999 1.540 ! (ex. 2,2-dimethylbutane) CH1 CH1 9999999999 1.540 ! (ex. 2,3-dimethylbutane) CH1 CT 9999999999 1.540 ! (ex. 2,2,3-trimethylbutane) CT CT 9999999999 1.540 ! (ex. 2,2,3,3-tetramethylbutane) ANGLES ! !V(angle) = Ktheta(Theta - Theta0)**2 ! !Ktheta: kcal/mole/rad**2 !Theta0: degrees ! ! Ktheta (kcal/mol) = Ktheta (K) * Boltz. const. ! !atom types Ktheta Theta0 CA3 CH2 CH2 31250 114.00 ! (ex. n-butane) CC3 CH2 CC3 31250 114.00 ! (propane only) CE3 CH2 CH1 31250 114.00 ! (2-methylbutane only) CH2 CH2 CH2 31250 114.00 ! (ex. n-pentane) CH2 CH2 CH1 31250 114.00 ! (ex. 2-methylpentane) CH2 CH2 CT 31250 114.00 ! (ex. 2,2-dimethylpentane) CH1 CH2 CH1 31250 114.00 ! (ex. 2,4-dimethylpentane) CH1 CH2 CT 31250 114.00 ! (ex. 2,2,4-trimethylpentane) CM3 CH2 CH1 31250 114.00 ! (ex. 3-methylpentane) CM3 CH2 CT 31250 114.00 ! (ex. 2,2-dimethylbutane) CD3 CH1 CD3 31250 109.47 ! (isobutane only) CE3 CH1 CE3 31250 109.47 ! (2-methylbutane only) CE3 CH1 CH2 31250 109.47 ! (2-methylbutane only) CH2 CH1 CH2 31250 109.47 ! (ex. 3-methylpentane) CH2 CH1 CH1 31250 109.47 ! (ex. 2,3-dimethylpentane) CH2 CH1 CT 31250 109.47 ! (ex. 2,2,3-trimethylpentane) CH1 CH1 CH1 31250 109.47 ! (ex. 2,3,4-trimethylpentane) CK3 CH1 CH2 31250 109.47 ! (ex. 2-methylpentane) CK3 CH1 CH1 31250 109.47 ! (ex. 2,3-dimethylbutane) CK3 CH1 CK3 31250 109.47 ! (ex. 2,3-dimethylbutane) CK3 CH1 CT 31250 109.47 ! (ex. 2,2,3-trimethylbutane) CG3 CT CG3 31250 109.47 ! (2,2-dimethylpropane only) CJ3 CT CJ3 31250 109.47 ! (2,2-dimethylbutane only) CJ3 CT CH2 31250 109.47 ! (2,2-dimethylbutane only) CK3 CT CK3 31250 109.47 ! (ex. 2,2-dimethylpentane) CK3 CT CH2 31250 109.47 ! (ex. 2,2-dimethylpentane) CK3 CT CH1 31250 109.47 ! (ex. 2,2,3-trimethylbutane) CH2 CT CH2 31250 109.47 ! (ex. 3,3-dimethylpentane) CH2 CT CH1 31250 109.47 ! (ex. 2,3,3-trimethylpentane) CH3 CT CT 31250 109.47 ! (2,2,3,3-tetramethylbutane) DIHEDRALS ! !V(dihedral) = Kchi(1 + cos(n(chi) - delta)) ! !Kchi: kcal/mole !n: multiplicity !delta: degrees ! ! Kchi (kcal/mol) = Kchi (K) * Boltz. const. ! Boltzmann = 0.0019872041 kcal / (mol * K) ! ! NERD Inherits most of its dihedrals from OPLS UA ! !atom types Kchi n delta description X CH2 CH2 X 0.00 0 0.0 ! NERD/OPLS (ex. n-butane) X CH2 CH2 X 355.04 1 0.0 ! "" X CH2 CH2 X -68.19 2 180.0 ! "" X CH2 CH2 X 791.32 3 0.0 ! "" X CH2 CH1 X 1416.3 0 0.0 ! NERD/OPLS (ex. 2-methylbutane) X CH2 CH1 X 398.3 1 0.0 ! "" X CH2 CH1 X 139.12 2 180.0 ! "" X CH2 CH1 X -901.2 3 0.0 ! "" X CH1 CH1 X 1635.7 3 0.0 ! NERD/OPLS (ex. 2,3-DMBut) X CT CH2 X 1635.7 3 0.0 ! NERD/OPLS (ex. 2,2-DMBut) X CT CH1 X 1635.7 3 0.0 ! NERD/OPLS (ex. 2,2,3-TriMBut) X CT CT X 2950.91 0 0.0 ! this work X CT CT X -2047.06 3 0.0 ! (2,2,3,3-tetramethylbutane) X CT CT X 529.25 6 180.0 ! "" X CT CT X 150.16 12 0.0 ! "" NONBONDED_MIE ! !V(mie) = 4*eps*((sig_ij/r_ij)^n-(sig_ij/r_ij)^6) ! !atom eps sig_ij n description CH4 148.00 3.730 12 ! NERD (note, same as TraPPE) CA3 104.00 3.910 12 ! (general case) CB3 100.60 3.825 12 ! (ethane) CC3 102.60 3.857 12 ! (propane) CD3 78.23 3.880 12 ! (isobutane) CE3 79.50 3.900 12 ! (2-methylbutane) CG3 74.50 3.910 12 ! (2,2-dimethylpropane) CJ3 74.50 3.870 12 ! (2,2-dimethylbutane) CK3 70.00 3.850 12 ! (methyl side chain) CM3 83.00 3.820 12 ! (ethyl side chain) CH2 45.80 3.930 12 ! CH1 39.70 3.850 12 ! CT 17.00 3.910 12 !