Electronic and Optical Properties of Sodium Niobate: A Density Functional Theory Study

Table 3

Structural properties of the orthorhombic phase of NaNbO₃.

	PBE	PBEsol	AM05	Experiment
a (Å)	5.558	5.496	5.514	5.505 [37]
				5.506 [6]
b (Å)	5.625	5.562	5.580	5.569 [37]
				5.566 [6]
c (Å)	15.670	15.494	15.545	15.519 [37]
				15.520 [6]
(Å^3)	489.903	473.632	478.290	475.771 [37]
				475.632 [6]
(GPa)	105.1	117.1	108.9	157.5 [38]
(GPa)	5.4	6.8	6.9	4.0 [38]
(eV)	2.360	2.298	2.298	3.45 [34]
(meV)	−108	−109	−94	—

Given are the lattice parameters a, b, and c, the equilibrium unit-cell volume , the bulk modulus and its pressure derivative , and the direct (-) Kohn–Sham energy gaps , respectively, calculated with different exchange-correlation functionals. The last row gives the energy difference per functional unit cell with respect to the high-temperature simple cubic perovskite phase.