Urey-Bradley PotentialΒΆ
Urey-Bradley potential energy accounts for the 1-3 nonbonded interactions. The cubic and quartic terms are added to the harmonic functional form in Tinker:
\[U = k\Delta u^2(1 + k_3\Delta u + k_4\Delta u^2),\]
where \(\Delta u\) is the difference of 1-3 distance deviating from its ideal value. Coefficients k3 and k4 are usually zero.