Novel lithium-nitrogen compounds at ambient and high pressures

Area of Science:

• Computational Materials Science
• Solid-State Chemistry
• High-Pressure Physics

Background:

• The behavior of lithium-nitrogen (Li-N) compounds under pressure is not fully understood.
• Previous theoretical and experimental studies on Li-N systems have presented conflicting results.

Purpose of the Study:

• To predict novel stable lithium-nitrogen compounds using ab initio evolutionary simulations.
• To investigate the structural and electronic properties of these compounds at high pressures.
• To resolve existing controversies regarding Li-N compound structures.

Main Methods:

• Ab initio evolutionary simulations were employed to explore the Li-N phase diagram.
• Density Functional Theory (DFT) calculations were used to determine structural stability and electronic properties.
• Analysis of electron counting rules and electronic band structures was performed.

Main Results:

• Five new stable Li-N compounds (Li13N, Li5N, Li3N2, LiN2, and LiN5) were predicted at pressures up to 100 GPa.
• Diverse nitrogen structures were observed, including isolated atoms, N2 dimers, N chains, and N5 rings.
• The Li13N structure features unique Li12N icosahedra not predicted by Wade-Jemmis rules.
• Electronic structures exhibit significant pressure and composition dependence, showing metal-insulator transitions.
• The study resolves previous theoretical and experimental discrepancies concerning Li2N2.

Conclusions:

• The Li-N system hosts a rich variety of stable compounds with unique structural motifs.
• Pressure-induced electronic structure changes in Li-N compounds provide a platform for studying metal-insulator transitions.
• This work establishes a more complete understanding of the Li-N phase diagram and resolves long-standing scientific debates.