Geometric and electronic structures of Al_nCu_m (n = 5–9, m = 1–3) clusters: genetic algorithm combined with ab initio models

Abstract

The geometries, stabilities and electronic structures of Al_nCu_m (n = 5–9, m = 1–3) clusters were explored by using the genetic algorithm combined with ab initio methods. The geometric structures are almost spherical when the valence electrons are around the magic number 20, otherwise the structures are oblate or prolate. The stabilities of the clusters are related to both the Cu/Al ratios and the electronic configurations. The clusters with lower Cu/Al ratios have high stabilities. The molecular orbitals are in accord with the shell structures predicted by the jellium model. The 3d orbitals of the Cu atoms are localised, although their orbital energies are between the 1P and 1D jellium orbitals. The Al₆Cu₂ with 20 valence electrons forms closed 1S²1P⁶1D¹⁰2S² shells, and shows large binding energy and removal energy, large ionisation potential and small electron affinity. For the no-magic clusters, the structure deformation leads to crystal-field-like splitting of the degenerate shells and stabilises the clusters.

GRAPHICAL ABSTRACT

KEYWORDS:

• Al_nCu_m (n = 5–9, m = 1–3)
• genetic algorithm
• Ab initio method
• stability
• electronic structures

Acknowledgment

We appreciate Jijun Zhao for offering the GA code. We also thank Tianhe and Shenzhen Computing Centers for computation resources.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China (grant number 11804264, 11947080, 11664034 and 11847146), Doctoral Program of Xi’an Aeronautical University (2018KY0205, 2018KY0206, 2018KY0207), College Students Innovations Special Project (S201911736023, DCX2019043), and Special Scientific Research Program supported by Shaanxi Education Department (No. 19JK0429).