Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory

Table 5

Lattice parameter , angle , equilibrium unit-cell volume , atomic displacements in percent of , and total-energy difference per formula unit with respect to cubic calculated with different exchange-correlation functionals for the rhombohedral phase of . Data in brackets represent relative deviations from the experimental values in percent.

R3m	LDA	PBE	PBEsol	AM05	RTPSS
(Å)	3.961 ()	4.059 ()	4.001 ()	4.014 ()	4.027 ()	4.016
(°)	89.95 ()	89.80 ()	89.90 ()	89.86 ()	89.95 ()	89.92
()	62.15 ()	66.87 ()	64.05 ()	64.67 ()	65.30 ()	64.77
K	1.296	2.281	1.794	2.046	2.037	1.300
Nb	0	0	0	0	0	0
O1	3.340	5.548	4.360	4.945	4.580	0.301
O2	3.340	5.548	4.360	4.945	4.580	0.333
O3	3.340	5.548	4.360	4.945	4.580	0.333
(eV)

[41]; measured at 230 K.