Initial estimate for minimum energy pathways and transition states using velocities in internal coordinates

Abstract Many reaction pathway finding algorithms require an initial estimate of the minimum energy path (MEP). This initial estimate is usually computed variationally and must be seeded from an even simpler path, where care must be taken to avoid atomic intersections. As an alternative, we estimate the MEP by integrating a velocity vector projected from redundant internal coordinates into the Cartesian manifold. We compare this method to the image dependent pair potential, the geodesic method, linear synchronous transit, and linear Cartesian interpolation. In our first test, rotation of a methyl group in ethane, a zero-temperature string calculation seeded with our method converged to the MEP significantly faster than from any other method. In our second test, HCN → HNC tautomerization, only the geodesic method slightly outperformed ours. In the third test, HONO elimination from dimethylnitramine, our method produced an estimate for the transition state that was geometrically the closest to the true transition state and converged the fastest.