I see even the most simple force field (Dreading) need bond order specification.
But e.g. gaff2 does not work with bond order at all so single autobond created are OK (because gaff2 identify forces base don atom types) … Correct ?
Question:
Can I specify only the bonds in the asymmetric unit cell part and let GULP generate the rest of the cell by symmetrically related molecules with identical bond types ?
Under the assumption there are no cross-symmetry, inter cell bonds ?
I am afraid this is impossible because GULP can not utilize the correct information about bonding in the asymmetric unit to fill the whole cell … Correct ?
Otherwise for automatic generation in gulp, I must give each atom a specific label and specify the bond type to the other labeled atom … And create a huge force-field translation table translating all labels to FF types … Correct ?
Dreiding (note spelling as dreading is an amusing way of describing it, assuming you really don’t like this force field!) isn’t the simplest force field as a Lennard-Jones plus Coulomb be simpler. If you specifically say “molecular force field” then you come closer.
If you specify the right atom types in the asymmetric unit then you can set all the bonds to the right type with the “bondtype” option and automatic bonding generation.
Thank you for your explanation. The miss spell of the Dreiding was non-intentional. It is a nice force field suitable for different MM engines comparison.
I can confirm that with GULP 6.3.1. I am able to get 100% identical results for a structure entered in space group P212121 with bonds defined by sequence like in my case:
and Materials Studio GULP run in space group P1 with all bonds pre-generated by Materials Studio.
Dreiding ff, Gasteiger charges (Antechamber versus MS engine), automatic atom types assignment (Antechamber versus MS engine with manual correction for the X_R non standard behavior)
The 100% correspondence was confirmed by CIF analysis in Mercury (Crystal Packing Similarity) …
I can now work on 100% automatization of this process (for Dreiding, UFF, gaff ,gaff2).
If you want eventually put such test in your examples, the .gin file follows: