H·(H₂O)_n Clusters: Microsolvation of the Hydrogen Atom via Molecular ab Initio Gradient Embedded Genetic Algorithm (GEGA)

Abstract

A new version of the ab initio gradient embedded genetic algorithm (GEGA) program for finding the global minima on the potential energy surface (PES) of mixed clusters formed by molecules and atoms is reported. The performance of the algorithm is demonstrated on the neutral H·(H(2)O)(n) (n = 1-4) clusters, that is, a radical H atom solvated in 1-4 water molecules. These clusters are of a fundamental interest. The solvated hydrogen atom forms during photochemical events in water, or during scavenging of solvated electrons by acids, and transiently exists in biological systems and possibly in inclusion complexes in the deep ocean and in the ice shield of earth. The processes associated with its existence are intriguingly complex, however, and have been the subject of decades-long debates. Using GEGA, we explicate the apparently extreme structural diversity in the H·(H(2)O)(n) (n = 1-4) clusters. All considered clusters have four basic structural types: type I, where the H radical is weakly coordinated to the oxygen atom of one of the water molecules; type II, where H is weakly coordinated to a H atom of one of the water molecules; type III, consisting of H(2), the OH radical, and n - 1 H(2)O molecules; and type IV, consisting of H(3)O and n - 1 H(2)O. There are myriads of isomers of all four types. The lowest energy species of types I and II are the isoenergetic global minima. H·(H(2)O)(n) clusters appear to be a challenging case for GEGA because they have many shallow minima close in energy some of which are significantly less stable than the global minimum. Additionally, the global minima themselves have high structural degeneracy, they are only weakly bound, and they are prone to dissociation. GEGA performed exceptionally well in finding both the global and the low-energy local minima that were subsequently confirmed at higher levels of theory.

Global optimization of clusters using electronic structure methods

“…Genetic algorithm Main-group elements and coinage metals Li, [117] Cs, [119] B, [118] Al, [138] Ga, [139] Si, [140] Sn, [130,[134][135][136] Pb, [141] P, [142] As, [142] Bi, [143] Cu, [126,144] Ag, [94,125,126] Au [94,125,126,145] Nanoalloys Na-Si, [127] Sn-Bi, [146,147] Ag-Cu, [126] Au-Cu, [126] Au-Ag [94,125] Oxide a and other systems Li-O, [148] Be-O, [149] Mg-O, [150,151] B-O, [152] Al-O, [153] Ce-O, [154] W-O, [155] Li-F, [156] Al-H, [157] B-C, [158] Li-Al-B, [159] H 2 O-H [160] Complex systems Ag-Lig, [161] Au-Surf, [131,162] Au-Pd-Surf [162] Basin hopping Homoatomic B, <...>…”

Li7(BH)5+: a new thermodynamically favored star-shaped molecule

“…The search was performed employing the GEGA program, 35,36 using the PBE0 functional 37 and the Stuttgart/Dresden effective core potential (ECP) 38 with its respective SDD basis set for geometry optimizations. The global minima and the 30 kcal/mol lowest-energy isomers were re-optimized and characterized with the same functional and cc-pVTZ 38 basis set implemented in the Gaussian 09 program.…”

(Li6Si5)2–5: The Smallest Cluster‐Assembled Materials Based on Aromatic Si56− Rings

“…GM structures of (Li 5 Si 5 ) 2 2− (Li 6 Si 5 ) 2 and (Li 7 Si 5 ) 2 2+ clusters, according to our global optimization algorithms, are depicted in Figure a. The most striking result is that these dimers preserve key structural patterns from the monomers .…”