Hello all,
I am trying to model molecular crystals like 4-iodo-4'-nitrobiphenyl (INBP) (Fdd2) crystals, starting with a supercell (1*3*3) to calculate interaction energies between molecules using the module Discover, I am getting very high and positive energies (total energy of the supercell and the energy of different faces calculated using the interaction energies between molecules) . I have used the force field Compass with group based cutoff for both Coulombic and Van der Waals interactions.
Is this just a problem of convention and this higher (more positive) value of the energy indicates a more favorable state, means 17846.763816 kcal/mol will be presented as -17846.763816 kcal/mol which is the correct energy physically for my system? I have also studied the influence of the optimization of the structure where the lattice was kept fixed, and after a successful completion the total energy was still positive!
can you please tell me what could this energy be interpreted?
FORCEFIELD OPTIONS
__________________
Filename : compass.frc
Definition name : cff91
Version : 2.8
Last modification date : 3/6/2007
# of automatic parameters : 3
NONBOND ENERGY CUTOFFS
______________________
Cutoff (A) Spline Width (A) Buffer Width (A)
vdW 60.00 20.00 8.00
Coulomb 60.00 20.00 8.00
Summation method for vdW : Group based
Summation method for Coulomb : Group based
Dielectric : 1.00
NOTE: Pressure and energy tail corrections will be added to all subsequent energy evaluations
Energy components kcal/mol
Total: 17846.763816
Internal: 16721.509682
Bond: 9573.893440
Angle: 178.920925
Torsion: 7447.386241
OutOfPlane: 0.002505
Cross: -478.693430
BondBond: 51.136997
BondAngle: -231.007897
EndBondTorsion: 0.922548
MiddleBondTorsion: -566.108165
AngleTorsion: 277.569763
AngleAngleTorsion: 4.160814
BondBond-1-3: -15.367491
AngleAngle: 0.000000
Nonbond: 1126.000378
Vdw: -739.607305
Repulsive: 5615.276611
Dispersive: -6354.883917
Electrostatic: 1865.607683
Hydrogenbond: 0.000000
Restraint: -0.746244
BtclRestraint: -0.746244
After minimization:
| MINIMIZATION ENERGY SUMMARY | ||
| ___________________________ | ||
| Initial | Final | |
| ------- | ----- | |
| Total Potential energy | 17906.343 | 8375.45931 |
| Internal | 16717.5577 | 7439.85051 |
| bond | 9573.88526 | 313.143185 |
| angle | 178.810648 | 219.447534 |
| torsion | 7444.4768 | 7456.73648 |
| out_of_plane | 0.002505 | 0.731331 |
| cross | -479.617545 | -550.208027 |
| bond_bond | 51.125032 | 5.729022 |
| bond_angle | -231.091265 | -20.643667 |
| end_bond_torsion | 0.922548 | -225.299425 |
| middle_bond_torsion | -566.108165 | -439.07899 |
| angle_torsion | 276.759737 | 140.425759 |
| angle_angle_torsion | 4.142058 | -0.304737 |
| bond_bond_1_3 | -15.367491 | -11.035988 |
| angle_angle | 0 | 0 |
| torsion_torsion | 0 | 0 |
| oop_oop | 0 | 0 |
| nonbond | 1189.83419 | 936.657631 |
| vdW | -718.435306 | -887.356917 |
| vdW_repulsive | 5515.14887 | 5297.42028 |
| vdW_dispersive | -6233.58417 | -6184.7772 |
| electrostatic | 1908.2695 | 1824.01455 |
| hydrogenbond | 0 | 0 |
| restraint | -1.04883 | -1.04883 |
| tethering_restraint | 0 | 0 |
| distance_restraint | 0 | 0 |
| angle_restraint | 0 | 0 |
| torsion_restraint | 0 | 0 |
| oop_restraint | 0 | 0 |
| chiral_restraint | 0 | 0 |
| btcl_restraint | -1.04883 | -1.04883 |
Thank you in advance.
Regards
