Quantum Monte Carlo study of small aluminum clusters Aln(n=2–13)

Abstract

Using fixed node diffusion quantum Monte Carlo (FN-DMC) simulations and density functional theory (DFT) within the generalized gradient approximations, we calculate the total energies of the relaxed and unrelaxed neutral, cationic, and anionic aluminum clusters, Al n (n = 1-13). From the obtained total energies, we extract the ionization potential and electron detachment energy and compare with previous theoretical and experimental results. Our results for the electronic properties from both the FN-DMC and DFT calculations are in reasonably good agreement with the available experimental data. A comparison between the FN-DMC and DFT results reveals that their differences are a few tenths of electron volt for both the ionization potential and the electron detachment energy. We also observe two distinct behaviors in the electron correlation contribution to the total energies from smaller to larger clusters, which could be assigned to the structural transition of the clusters from planar to three-dimensional occurring at n = 4 to 5.

Binding energies of small lithium clusters: A comparison of different theoretical calculations

“…In comparison with the DMC binding energy given in Figure 2, we find that the electron correlation has a very large contribution to the binding energy varying from 58% to 83% of its total value. It also shows that E BE /BE is sensitive to the cluster structure and exhibits an even-odd alternation pattern being similar to those observed in some properties of metal clusters such as the electron binding energy for open and closed shell aluminum clusters [29], indicating that the Li n clusters of even-number size are relatively more favored in terms of correlation energy than the neighbors of odd-number size.…”

“…In this case, our results are in agreement with the CCSD(T) calculations by Wheeler et al [13] and support the monotonic increasing in binding energies per atom observed in Wu's experiments [5] though their binding energies are consistently larger than ours. The correlation energy of a cluster can be obtained by the difference between the DMC and HF energies calculated at a converged basis set [29], E c = E DMC − E HF . Figure 3 shows the correlation energy of the Li n clusters as a function of the cluster size.…”

Density Functional Theory Assessment of Molecular Structures and Energies of Neutral and Anionic Aln (n = 2–10) Clusters

“…In addition, a recent quantum Monte Carlo (QMC) study also reported sharp minimum behavior in the vIE of Al n calculations. 53 On the other hand, no DFT functionals used in this study give the minimum value of vIE on Al 7 . All DFT functionals except B3LYP show that the vIE of Al 10 is the minimum for clusters ranging from Al 2 to Al 10 .…”

Quantum monte carlo study of the energetics of small hydrogenated and fluoride lithium clusters

“…DMC is the appropriate tool do deal with systems for which electron correlation plays important role. It can achieve accuracy similar to the best quantum chemistry methods with some advantages like allowing better scaling for medium to large size systems and providing quantum statistical errors . The importance of correlation effects on the energetics and the relative stability of the clusters is investigated.…”