Hello,

I am trying to build a composite silicone-gel model containing an Al₂O₃ nanoparticle using Materials Studio 2020 and the Forcite module. The polymer matrix is modeled with the COMPASS force field, and I need to keep the same force field for the composite system.

The Al₂O₃ nanoparticle was obtained from the structure library and cut from a periodic oxide structure. The current cluster contains 26 Al atoms, 38 O atoms, and 2 H atoms. Al–O bonds are present in the structure.

When I assign the COMPASS force field and run an Energy calculation or Geometry Optimization, Materials Studio reports missing parameters:

Bond Stretch:
(al3o o_al), (o2z al3o)

Angle Bend:
(al3o o_al al3o), (o2z al3o o_al), (o_al al3o o_al)

Torsion:
(al3o o_al al3o o2z), (al3o o_al al3o o_al)

Inversion:
(al3o o_al o_al o_al), (o_al al3o al3o al3o)

The calculation can still terminate normally, but the Al–O bonded energy contributions are incomplete or zero. Therefore, I do not consider the result reliable for Geometry Optimization, annealing, NPT, or NVT simulations.

The atom types are assigned as, for example:

Al: al3o
O: o_al or o2z

I also tested the Universal force field, and the calculation can run without missing parameters. However, I must use COMPASS for consistency with the silicone-gel matrix.

I found a 2023 paper describing the INTERFACE force field. It provides IFF-PCFF parameters for α-Al₂O₃, including charges and 9–6 Lennard-Jones parameters, and states that the model can be combined with PCFF/COMPASS-type organic force fields. However, I cannot find an option in Materials Studio 2020 to edit or import custom bonded/nonbonded parameters through the Forcite interface.

My questions are:

1. Does Materials Studio 2020 support custom COMPASS force-field parameter editing or .frc file modification?
2. Is it possible to use COMPASS for the polymer while treating Al₂O₃ as a rigid, non-bonded inclusion?
3. If so, should the Al–O bonds be deleted only after COMPASS atom types and charges have been assigned?
4. Would deleting the Al–O bonds allow Forcite to calculate the composite system using only electrostatic and van der Waals interactions?
5. Is there a recommended procedure for implementing IFF-PCFF or IFF-PCFF-HQ parameters in Materials Studio 2020?
6. Does a newer version of Materials Studio provide a supported interface for adding these parameters?

I would appreciate any advice or examples of successfully modeling Al₂O₃/silicone or Al₂O₃/polymer composites using COMPASS or PCFF in Materials Studio.