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bhavinbhavin 

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
 
CarstenCarsten (Accelrys) 
There is no absolute zero for forcefields and you may get positive values.

When the structure significantly changed during the optimization please redo the QEq and do another geometry optimization.
bhavinbhavin
Thanks for the reply!

I repeatedly performed geometry optimization but it doesn't help significantly.

Have attached the .xsd file.