The ionic versus metallic nature of 2D electrides: a density-functional description

Area of Science:

• Materials Science
• Condensed Matter Physics
• Quantum Chemistry

Background:

• Two-dimensional (2D) electrides are rare materials with interstitial electron layers between cationic atomic layers.
• Only two such materials, [Ca2N]+e− and [Y2C]2+(2e−), are experimentally known.
• Understanding their mechanical properties like exfoliation and sliding is crucial for potential applications.

Purpose of the Study:

• To investigate the exfoliation and interlayer sliding properties of the two known 2D electrides.
• To understand the role of interstitial electrons and ionic bonding in these properties.
• To assess the accuracy of density-functional theory with dispersion corrections for 2D electrides.

Main Methods:

• Density-functional theory (DFT) calculations.
• Inclusion of exchange-hole dipole moment dispersion correction (a system-dependent dispersion correction).
• Analysis of valence states, exfoliation energies, and interlayer sliding barriers.

Main Results:

• Calculated exfoliation energies for 2D electrides are significantly higher than for typical 2D materials.
• Interlayer sliding barriers are low, comparable to conventional 2D materials, and insensitive to dispersion corrections.
• Intercalated electrons in bulk and surface states in expanded forms were identified.
• The ionic nature and strong Coulomb forces contribute to high exfoliation energies.

Conclusions:

• 2D electrides possess unique mechanical properties: high exfoliation energy and low sliding barrier.
• The metallic nature of interstitial electrons likely facilitates layer mobility.
• Accurate DFT treatment requires system-dependent dispersion corrections for reliable predictions.