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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.