Positive total energy

Hello Everyone,

I am using Forcite (Geometry optimization) to minimize an organic molecular structure (CCDC reference name: PUVRIH).

However, after the optimization, total energy comes out to be a ‘positive’ term instead of commonly observed negative values. It seems I am doing something wrong here. Can anyone please guide me ?

Parameters used for minimization are as follows:


Force field: Dreiding
Charges: QEq
Quality: Ultrafine
Electrostatic: Ewald
van der Waals: Atom based
Algorithm: Smart
Max iterations: 1000000
Optimize cell has been checked too.

Results observed:

---- Initial structure ----

 

Total enthalpy : 359.295788 kcal/mol

External pressure term : 0.000000 kcal/mol

 

Total energy : 359.295788 kcal/mol

 

Contributions to total energy (kcal/mol):

Valence energy (diag. terms) : 249.591

Bond : 203.474

Angle : 40.674

Torsion : 4.859

Inversion : 0.583

Non-bond energy : 109.705

Hydrogen bond : 0.000

van der Waals : 100.922

Long range correction : -0.861

Electrostatic : 9.644

 

rms force : 5.523E+001 kcal/mol/A

max force : 1.208E+002 kcal/mol/A

rms stress : 2.027E+000 GPa

max stress : 3.468E+000 GPa

 

Cell parameters: a: 8.759000 A b: 10.554000 A c: 10.606400 A

alpha: 114.116 deg beta: 96.957 deg gamma: 97.535 deg

 

---- Final structure ----

 Total enthalpy : 131.924374 kcal/mol

External pressure term : 0.000000 kcal/mol

Total energy : 131.924374 kcal/mol

Contributions to total energy (kcal/mol):

Valence energy (diag. terms) : 75.409

Bond : 28.981

Angle : 43.902

Torsion : 2.058

Inversion : 0.468

Non-bond energy : 56.515

Hydrogen bond : 0.000

van der Waals : 43.804

Long range correction : -0.815

Electrostatic : 13.527

rms force : 1.986E-004 kcal/mol/A

max force : 8.959E-004 kcal/mol/A

rms stress : 1.161E-005 GPa

max stress : 2.586E-005 GPa


Thanks,
Bhavin