A diatomics-in-molecules case study on the system Be+HF→BeF+H. II. The sensitivity of the potential surfaces to the diatomic input

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Abstract
Potential energy surfaces are presented for a series of diatomics-in-molecules (DIM) models of the reaction Be+HF→BeF+H. This system involves low-lying electronic states of Be and ionic contributions to bonding and is therefore quite complex from the DIM point of view. The various DIM models involve between three and 18 structures and make extensive use of configuration interaction in the diatomic fragments. The potential surface is predicted to have a barrier ∼1.9 eV high for collinear BeFH; at bent configurations this barrier gradually increases. A potential surface having this feature is obtained only if the Be(2s2p) configuration is included in the DIM model. The general problem is raised of how to decide whether a given structure in a DIM model should be retained or not, and of how best to obtain reliable diatomic configuration interaction input data.