Force Field X – Force Field Properties

Force Field Properties

Force Field properties are used to specify the functional form of the force field, including bonded terms, van der Waals and electrostatics.

Property	Type	Default	Description
bondterm	boolean	true	Specifies use of the bonding term for the AMOEBA potentials.
angleterm	boolean	true	Specifies use of the angle bending term for the AMOEBA potentials.
mpoleterm	boolean	true	Controls use of the permanent multipole electrostatics term for the AMOEBA potential. Setting `mpoleterm` to false also turns off polarization, overriding the polarizeterm property below.
opbendterm	boolean	true	Specifies use of the out-of-plane bending term for atoms at trigonal centers under the AMOEBA potentials.
pitorsterm	boolean	true	Specifies use of the pi-torsion term between atoms that have double bond character under the AMOEBA potentials.
polarizeterm	boolean	true	Controls use of polarizable electrostatics for the AMOEBA potential. Setting `polarizeterm` to false overrides the polarization property below.
polarization	string	mutual	[mutual/direct/none] `Mutual` indicates the induced dipoles on each atom interact self-consistently. `Direct` indicates that induced dipoles are influenced by the permanent multipoles, but not each other. `None` turns off polarization.
polar-eps	double	1.0e-6	This is the convergence criteria for the self-consistent field calculation in units of RMS Debye. The default of 1e-6 is necessary for optimizations to a tight tolerance. For optimization during X-rey refinement to an RMS gradient per atom of 0.1, then a looser `polar-eps` of 1e-3 is sufficient. For molecular dynamics with a thermostat, 1e-2 is resonable trade-off between accuracy and performance.
polar-sor	double	0.70	Calculation of the self-consistent field is based on successive over-relaxtion (SOR). The `polar-sor` parameter controls the fractional change in the induced dipoles that is accepted prior to the beginning of the following iteration. The default value of 0.70 does not usually need to be changed, although in rare cases a slightly more conservative value of 0.65 is necessary.
strbndterm	boolean	true	Specifies use of the stretch-bend bond-angle coupling term for the AMOEBA potentials.
torsionterm	boolean	true	Specifies use of Fourier series torsional terms for AMOEBA potentials.
tortorterm	boolean	true	Specifies use of spline based torsion-torsion terms for AMOEBA protein and nucleic acid force fields.
ureyterm	boolean	true	Specifies use of the Urey-Bradley restraint between water hydrogen atoms for the AMOEBA water model.
vdwterm	boolean	true	Specifies use of the Buffered-14-7 van der Waals potential for the AMOEBA force field. If set to `false`, all non-bonded terms are turned off.