R. Polák

Atoms-in-molecules calculations on diatomic fragments of polyatomic systems. HeH and HeH+

Abstract Two different modifications of the atoms-in-molecules method are applied to various states of the HeH and HeH + species. The calculations are carried out in a wide range of internuclear separations in order to obtain a description of the diatomics adequate to serve as input for a subsequent DIM calculation of potential energy surfaces of (HeH 2 ) + . The results are compared with other presently available calculations.Abstract Two different modifications of the atoms-in-molecules method are applied to various states of the HeH and HeH + species. The calculations are carried out in a wide range of internuclear separations in order to obtain a description of the diatomics adequate to serve as input for a subsequent DIM calculation of potential energy surfaces of (HeH 2 ) + . The results are compared with other presently available calculations.

DIM model calculations for (O2H)+ interaction potentials

Abstract Several low-lying potential energy surfaces for the (O 2 H) + system have been estimated using the diatomics-in-molecules (DIM) approach in a model calculation calibrated with known ab initio information. Main features of ground and lower excited states are qualitatively well reproduced in spite of the fact that the DIM basis was kept rather small. The error from the truncation of the basis set had to be compensated for by empirical adjustments of some of the input diatomic potential energy curves of the excited states. From the topography and crossing behaviour of the resulting potential energy surfaces some predictions concerning the mechanism of inelastic and charge transfer collisions are made.

Diatomics-in-molecules correlation diagrams for (BH2)+

Abstract The diatomics-in-molecules method is applied to calculate potential energy surfaces of the system B + ( 1 S, 3 P) + H 2 (X 1 Σ g + . Results are presented as correlation diagrams following the approximate minimum energy paths for C ∞v and C 2v geometries of the reactants. Two possible non-adiabatic mechanisms of complex formation are discussed.

Atoms-in-molecules calculations on diatomic fragments of polyatomic systems. FH and FH+

Abstract Two versions of the atoms-in-molecules method (the original Moffitt scheme and the orthogonalized Moffitt method) are applied to various states of the FH and FH − species to obtain information on diatomic state mixing and potential energy curves needed for a diatomic-in-molecules calculation on (FH 2 ) + .

Surface crossing in interaction of atomic hydrogen with a lithium metal cluster

Abstract Interaction of atomic hydrogen with a (4,1,4) lithium cluster, simulating the (100) metal surface, is studied using the diatomics-in-molecules method. Ground-and excited-state potential curves for normal approach ofH to some attack positions on the surface intersect or pseudo-intersect. The results reveal possible non-adiabatic character of the absorption process.

Diatomics-in-molecules potential energy surfaces of (HeH2)+: An extended basis set calculation

Abstract Within the framework of the non-hermitean DIM formulation of Tully and Truesdale, and using 13 symmetry-adapted polyatomic basis functions, ground-state and excited-state potential energy surfaces for (HeH 2 ) + have been calculated. Whereas the global shape of the potential energy surfaces is obtained in reasonable agreement with existing ab initio data, at least if scaling is introduced, there are marked differences in the details, e.g. the angular dependences and splitting of the first and second excited-state potential energy surfaces. The dependence of the results on mixing parameters and scaling as well as implications concerning the predictive power of the DIM method are discussed.

On the diatomic-fragment data calculation for the diatomics-in-molecules method. Applications to NH2 and NH3

Abstract This paper discusses the diatomics-in-molecules theory used in connection with diatomic input data generated by the atoms-in-molecules method and stresses the simplifications associated with the construction of mixed states. The methodical problems are exemplified by treating NH 2 and NH 3 , and conclusions are drawn concerning appropriate DIM models for these species.

Analysis of DIM energy hypersurfaces for some hydrogenic and lithium clusters

Abstract DIM ground state potential energy surfaces of three and four atomic lithium and hydrogenic clusters are analyzed from the viewpoint of the existence of stationary points. The results are compared with other presently available calculations using symmetry restricted optimizations.

An investigation of the importance of many-centre effects in the diatomics-in-molecules approach

Abstract An analysis of valence bond and diatomics-in-molecules calculations for H 3 performed within the same basis sets is used to study the salient features of the diatomics-in-molecules approach associated with neglect of more-centre terms, existency of non-hermitean eigenvalue equation and non-variational character of the solution.

Valence bond diatomics-in-molecules models of the NH2 radical

Abstract A valence bond diatomics-in-molecules model for the description of the ground and two excited valence states of NH2 has been developed. We find that, besides the N−(3Pg) ionic term and states associated with the 2s22p3 electron configuration, also structures involving the 4Pg(2s2p4) term of nitrogen are important for an adequate DIM model. Supplied with accurate diatomic potential energy and AIM mixing data, the DIM model is shown to behave in a qualitatively correct manner over the full range of nuclear configurations. Conclusions are drawn concerning the possible extension of the model to describe higher excited states.