Quantum Size Effect and Electronic Stability of Freestanding Metal Atom Wires

TL;DR

This study uses DFT calculations to analyze quantum size effects on the stability of freestanding metal atom wires, revealing oscillatory energy patterns linked to electron band filling and quantum confinement.

Contribution

It provides a detailed theoretical analysis of stability oscillations in metal atom wires, highlighting the role of electronic structure and quantum effects, which was not thoroughly explored before.

Findings

Total energy oscillates with wire length, indicating preferred lengths.

Even-odd oscillations in s-systems follow a decay law related to electron filling.

Complex oscillation patterns in sp-systems due to unpaired p orbitals.

Abstract

Using DFT calculations, we present a thorough study of the quantum size effects on the stability of freestanding metal atom wires. Our systems include Na, Ag, Au, In, Ga and Pb atom wires, i.e. $s$, $sd$, and $sp$ electron prototypes. We found that the total energy always oscillates with the wire length, which clearly indicates the existence of preferred lengths. Increasing the length, the s-system exhibits even-odd oscillations following a $a/x +b/x^2$ decay law in the stability, which can be attributed to electron band filling and quantum confinement along the wire. The $sd$-system exhibits a similar oscillation pattern, even in the presence of $sd$ hybridization. In $sp$-system, the energy oscillations are beyond the simple even-odd nature, likely due to unpaired p orbitals and the corresponding nontrival band filling. Our findings clearly demonstrate that electronic contribution is quite critical to the stability of freestanding wires, and this stability may be important even when wires are deposited on substrates or strained. This study sheds light on the underlying formation mechanism of metal atom wires.