[gmx-users] Potential energy positive. Can be?

[Eudes Fileti]

Hi gmx users,
I have tried to simulate a box with 1000 molecules of toluene
and I always have obtained a positive value for the potential energy.
I have used three different models of potential (with and without 14
interactions)
and all of them provides a positive value for energy. I must be falling in
some error or making some wrong analysis but I do not know what.
Below I put the average values that I got from the simulations that I made.
If somebody will be able to help me, I will be grateful!
Bests
eef

Two questions about these results:
# Why are so larger the values for LJ-14?
# How can I compose the potential energy from the components?
Would not be U = LJ + Coul + bond + ang + dihed ? And LJ-14?

        USING OPLS-UA with 14 interactions
        <======  ###############  ==>
        <====  A V E R A G E S  ====>
        <==  ###############  ======>

   Energies (kJ/mol)
           Bond          Angle  Improper Dih.          LJ-14     Coulomb-14
    1.74553e+04    2.86624e+03    1.04333e+04    6.20512e+04    0.00000e+00
        LJ (SR)  Disper. corr.   Coulomb (SR)      Potential    Kinetic En.
   -3.90255e+04   -4.73494e+03    2.98090e+01    4.90753e+04    2.62518e+04
   Total Energy    Temperature Pressure (bar)
    7.53271e+04    3.00743e+02   -3.32933e+00





        USING GMX with 14 interactions
        <======  ###############  ==>
        <====  A V E R A G E S  ====>
        <==  ###############  ======>

   Energies (kJ/mol)
           Bond          Angle  Improper Dih.          LJ-14     Coulomb-14
    1.75692e+04    3.90052e+03    8.64676e+03    5.45622e+04   -1.01334e+02
        LJ (SR)  Disper. corr.   Coulomb (SR)      Potential    Kinetic En.
   -4.84750e+04   -2.16220e+03   -8.82568e+01    3.38519e+04    2.62111e+04
   Total Energy    Temperature Pressure (bar)
    6.00630e+04    3.00276e+02    1.23474e+00





        USING OPLS-AA with 14 interactions
        <======  ###############  ==>
        <====  A V E R A G E S  ====>
        <==  ###############  ======>

   Energies (kJ/mol)
           Bond          Angle          LJ-14     Coulomb-14        LJ (SR)
    2.63123e+04    2.60679e+04    4.35409e+04   -1.94043e+04   -4.08125e+04
  Disper. corr.   Coulomb (SR)   Coul. recip.      Potential    Kinetic En.
   -1.39923e+03    7.83183e+02    8.19773e+03    4.32861e+04    5.65749e+04
   Total Energy    Temperature Pressure (bar)
    9.98610e+04    3.02436e+02    2.24669e+03






        USING OPLS-AA without 14 interactions
        <======  ###############  ==>
        <====  A V E R A G E S  ====>
        <==  ###############  ======>

   Energies (kJ/mol)
           Bond          Angle        LJ (SR)  Disper. corr.   Coulomb (SR)
    2.02244e+04    2.43199e+04   -4.04650e+04   -1.39923e+03    1.24955e+03
   Coul. recip.      Potential    Kinetic En.   Total Energy    Temperature
    8.38794e+03    1.23176e+04    5.56793e+04    6.79968e+04    2.97648e+02
 Pressure (bar)
    1.73270e+03


-- 
_______________________________________
Eudes Eterno Fileti
Centro de Ciência Naturais e Humanas
Universidade Federal do ABC
Rua Catequese, 242 - 3º Andar
09090-400  Santo André - SP Brasil
Tel: +55 11 4437-1600 ramal 408
skype: eefileti
http://cromo.ufabc.edu.br/~fileti/
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