Hi all,

Im a student and new to Materials studio.  Im working with defects in solid materials.

What i'd done was, initially, I used Forcite 'Geometry optimisation' to optimise my structure and to get my lattice energy values.  Then, I used GULP module to calculate my tensors and mechanical properties etc.  GULP does calculate lattice energy too, and the result generated between this two modules ( that i got) were completely different.  It might be caused by the different way each modules conduct its' calculation , but shouldnt the value approximately be the same? And also, I noticed there were differences in the values if I calculates using a cluster ( only the molecular structure) in comparison with the bulk structure ( build crystal).  The result I  got  for my system (Paracetamol) are:

Forcite:

Cluster :  15.676 kcal/mol

Bulk      :  -74.012 kcal/mol

GULP (P1 structure) :

Bulk  :   -55.8554 kJ/mol (13.35 kcal/mol)

I used the same charge set for all the calculations and I used the same forcefield which was Dreiding.  I used Materials studio 5.5. 

Im a little bit confused  right now Please if anyone can help me with this. 

Thanks a zillion.