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SousaSousa 

Multipole interactions

Hello  Dear MS users
I have a question about multipole interaction contributions. Would you please tell me that how are multipole-multipole interactions (such as dipole-dipole interactions) described in PCFF, COMPASS, cvff forcefields? Are they included in electrostatic coulomb interactions?

Best Regards
SJNS
Jason DeJoannisJason DeJoannis
Hi Sousa,
There are no multipole interactions in these forcefields. The interactions can be found in the Help under:

Theory > Classical simulations theory > Forcefields > Functional form

Yes, electrostatic energy is calculated purely from Coulombic interactions of point charges centered at each atom.

Best,
Jason
SousaSousa
Dear Jason,
Thank you for your reply. Accordingly, if a molecule (such as benzene with -1 charge or -2 charge) that have multipole moment, their multipole interaction will be calculated in columbic term of pcff, and it is not required to add a individual term of multipole-multipole interaction to pcff? 

Best Regards
Sousa
Jason DeJoannisJason DeJoannis
Sousa,
Why are you asking?

Benzene is not charged. But it, and other pi bonding molecules are polarizable, as noted in the paper: 
http://pubs.acs.org/doi/abs/10.1021/acs.jctc.6b00918

All of the forcefields in Forcite are fixed charge forcefields. It is not possible to use atomic dipoles, quadrupoles etc. It does not support many-body nonbond interactions (i.e. you will note that only pair potentials are in the list of Function Forms, with one exception).

GULP has some polarizable/multibody forcefields using either shell or EAM models.
SousaSousa
Dear Jason
Thank you for your guide. You are right, Benzene is not charged. But after some changings in its structure, we tried to charged it.
Then if  I understand correct, if I applied PCFF, all electrostatic interaction such as charge-charge, dipole-dipole, .....will be calculated by columbic term in PCFF based on partial charge interactions.
Best Regards
Sousa