Ab initiostudy of the stability of beryllium clusters: accurate calculations for Be_{2 − 6}

Abstract

We present results of theoretical investigation of the stability of small beryllium clusters, Be 2−6 . Due to the fact that the clusters are homonuclear, their stability is sufficiently represented by the binding energy D e calculated per atom. The knowledge of this quantity offers a possibility of calculating more complex energetic effects, such as destruction or fusion of the beryllium clusters and adding or detaching a beryllium atom. The most stable structures among those of the singlet multiplicity were studied using the highly correlated coupled clusters method with iterative single-and double-excitations and the perturbative triple excitations (CCSD(T)). The effect of electron correlation, basis set saturation, basis set superposition error, relativistic effects and the core correlation were carefully investigated and discussed. The optimized virtual orbital space (OVOS) with the controlled accuracy technique is extensively applied to alleviate the computational cost of calculations. In this specific case, the use of the OVOS technique led to speed-ups in computational time by more than an order of magnitude. Finally, we present the basis set extrapolated binding energies with all of the aforementioned corrections properly included, which are the most reliable data for this key property for Be 3−6 clusters to date. Furthermore, these values can serve as a valuable benchmark for testing the accuracy of less time consuming computational methods applicable for larger beryllium clusters.This paper is dedicated to Professor Alexander I Boldyrev on the occasion of his 60th birthday.

Ab initio study of many-body decomposition of the interaction energy in small beryllium clusters

“…In the case of Be 6 , other ground states, such as triplet [11] or quintet [19] are suggested in the literature. However, in our previous work [4] we have found the singlet state to be $0.4 eV more stable than the triplet state at the CCSD(T) level. The cluster geometries, taken from our previous work, [4] optimized at the MP2 level using augcc-pVTZ basis set, [20] are depicted in Figure 1.…”

“…However, in our previous work [4] we have found the singlet state to be $0.4 eV more stable than the triplet state at the CCSD(T) level. The cluster geometries, taken from our previous work, [4] optimized at the MP2 level using augcc-pVTZ basis set, [20] are depicted in Figure 1. Geometry optimizations were performed using the GAUSSIAN 03 program suite [21].…”

“…In accord with the electronic structure of the Be element, 1s 2 2s 2 , the Be 2 molecule is weakly bound, and can be considered as van der Waals species with the binding energy of 0.115 eV and the bond length 2.454 Å [3]. At this distance, our theoretical D e per atom is 0.0460 eV [4] using the same method as presented in this work. Consequently, it is difficult to achieve a convergence of properties of Be clusters toward the bulk limit [2,5].…”

“…Electron correlation effects are treated using the single reference MP2, CCSD and CCSD(T) methods with 1s Be core electrons frozen. The effect of the inner shell 1s electrons correlation was carefully examined in our previous work [4], as well as in Ref. [8].…”

A Theoretical Study of the X-Abstraction Reactions (X = H, Br, or I) from CH2IBr by OH Radicals: Implications for Atmospheric Chemistry

“…These relations can be used for specific application of the OVOS method for more efficient evaluation of BSSE, where OVOS is applied exclusively to the subsystems [67,77]. Reducing the VOS to the size of the subsystem in BSSE calculations, we typically encounter an error of 10 −5 -10 −4 a. u.…”