| Abstrakt: |
Global potential energy surfaces for the 1 4A′, 2 4A′, 1 4A″, and 2 4A″ spin-aligned states of Li3 are constructed as sums of a diatomics-in-molecules (DIM) term plus a three-body term. The DIM model, using a large basis set of 15 4A″ and 22 4A′ states, is used to obtain a “mixed-pairwise additive” contribution to the potential. A global fit of the three-body terms conserves the accuracy of the ab initio points of a full configuration-interaction calculation. The resulting fit accurately describes conical intersections for both the 1 4A′ and 2 4A′ surfaces with a root-mean-square (rms) deviation of 5.4×10-5 hartree in D∞h geometries and 1.2×10-4 hartree in C∞v geometries. The global fit appears to be quantitatively correct with a rms deviation of 1.8×10-4hartree for 1 4A′, 9.2×10-4 hartree for 2 4A′, 2.5×10-4 hartree for 1 4A″, and 5.1×10-4 hartree for 2 4A″. A possible diabolic conical intersection, also called an accidental degeneracy, in C2v geometries, indicating a seam of conical intersections in Cs geometries, is also found in ab initio calculations for A2 states. As shown in this example, the DIM procedure can be optimized to describe the geometric phase and nonadiabatic effects in multisurface potentials. [ABSTRACT FROM AUTHOR] |
