The Adiabatic-to-Diabatic Mixing Angle for B + H$_{2}$ Potential Energy Surfaces

The 1$^{2}A'$, 2$^{2}A'$, and 1$^{2}A''$ adiabatic potential energy surfaces and associated nonadiabatic coupling terms are calculated at the state-averaged MCSCF/CI level. A line integral through the nonadiabatic coupling terms is used to calculate the adiabatic-to-diabatic mixing angle required to transform from the 1$^{2}A'$ and 2$^{2}A'$ adiabatic basis to a corresponding diabatic basis. When all nonadiabatic coupling terms between all electronic states are considered, the line integral will be path independent. However, for our calculations, we consider only nonadiabatic coupling terms between the 1$^{2}A'$ and 2$^{2}A'$ states and the line integral is therefore path dependent. The path dependence of the line integral is then used to characterize the error introduced by employing a truncated set of adiabatic states. A method for reducing the effect of this error through the use of symmetry derived boundary conditions is discussed.