Parameters setup for first-principles on well-formedness and thermodynamic properties of bulk and habit surfaces of Mg₂Si

Abstract

The well-formedness, thermodynamic properties and mechanical properties of Mg2Si bulk and Mg2Si (1 0 0), (1 1 0) and (1 1 1) surfaces were calculated by using first-principles based on density functional theory (DFT). Some accurate and efficient parameters were programed by computing massively and repeatedly. The accurate and efficient parameters used in Mg2Si bulk is Energy cutoff (500 eV), k-point (5 × 5 × 5) and exchange-correlation interaction (PBEsol). The relaxation of surficial atoms shows that the rule or rate of expansion and shrink are similar from the second column. The rate of the innermost layer decreases gradually with increasing slab thickness. The rate of the innermost layer in Mg-terminated or Si-terminated Mg2Si (1 0 0) and (1 1 0) is no more than 0.1% when convergent layers are no less than 11. The convergent layers of Mg2-terminated and Si-terminated Mg2Si (1 1 1) are 14 and 16, respectively. The Mg1-terminated Mg2Si (1 1 1) surfaces hardly converge even if the layers reach to 18. Si-terminated surfaces are harder to keep stability than Mg-terminated surfaces in Mg2Si (1 0 0) and (1 1 1) surfaces because of a higher surface energy. Mg2Si (1 1 0) surface energy is a constant because of the nonpolar and stoichiometric Mg-Si terminated surface. Si-terminated and Mg-terminated Mg2Si (1 0 0) surfaces are more stable than Si-terminated and Mg2-terminated Mg2Si (1 1 1) surfaces, respectively. Mg1-terminated Mg2Si (1 1 1) surface is the most stable surface over the entire surfaces in Mg2Si.

Interplay between structural changes, surface states and quantum confinement effects in semiconducting Mg2Si and Ca2Si thin films

“…For the sake of comparison, the surface energy of Mg 2 Si(110) was also calculated and it turned out to be higher than the surface energy of Mg 2 Si(111) (see Table 1), which is consistent with the results in ref. 18 and 19. Hence, we do not further investigate Mg 2 Si thin films other than the cubic Mg 2 Si(111).…”

“…14 After that it was possible to grow thicker (50-400 nm) epitaxial Ca 2 Si(100) and Ca 2 Si(010) films by the molecular beam epitaxy method. 14 The up-to-date reported results of first-principles investigations of Mg 2 Si surfaces (in particular (100), ( 110) and (111) ones) [15][16][17][18][19] suggest that the Mg-terminated Mg 2 Si(111) surface possesses the smallest surface energy. 18,19 For the orthorhombic Ca 2 Si thin films there is only one study 20 where the surface energy and the appearance of surface states have been discussed for the (100), ( 010) and (001) slabs.…”

“…The comparison of the total energies of the orthorhombic and cubic Ca 2 Si slabs with thickness below 1.5 nm indicated a possibility to stabilize cubic Ca 2 Si(111) thin films. 6 However, previous theoretical studies 6,[15][16][17][18][19][20] did not focus on thickness-dependent properties (such as an influence of quantum confinement effects on the band-gap variation and changes in the band dispersion with thickness) of Mg 2 Si and Ca 2 Si thin films.…”