SiO2 forcefield

MASS
Si 28.08

BOND
O-Si 323.50 1.51 #gaff c3-ca

ANGLE
Si-O-Si 65.0 143.70 #gaff Si -> c3   # Vashishta et al -i made up the force constant 
O-Si-O  70.0 109.55 #gaff Si -> c3   # Vashishta et al -larger than C-Si-C force

DIHE
O-Si-O-Si 1 0.0 0.0 1. #gaff Si -> c3  -I set PK to zero, so torsional force is zero
Si-O-Si-O 1 0.0 0.0 1. #-PK set to zero, see above

IMPROPER

NONBON
Si 2.220 0.320 #DOCK vdw_AMBER_parm99.defn