LNO on STO LNO on LAO a b c b b c a b c b a Figure 3: Atomic structure of LNO grown on STO and LAO as determined by x-ray diffraction (Experiment) and density functional theory (Theory). In a ), the top data set corresponds to LNO/STO, while the bottom data set corresponds to LNO/LAO. The space group is C 2 /c (#15), with a = 9.406 ˚ A, b = c = 5.523 ˚ A, and a monoclinic angle of 125.95 ◦ for LNO/STO and a = 9.460 ˚ A, b = c = 5.367 ˚ A, and a monoclinic angle of 124.57 ◦ for LNO/LAO. The relation of the monoclinic unit cell ( a , b , c ) to the ideal perovskite ( a$_{p}$ , b$_{p}$ , c$_{p}$ ) is a$_{p}$ = c / √ 2, b$_{p}$ = b / √ 2, and c$_{p}$ = √ 6 a . b, Tensile strain from the STO substrate reduces the γ rotation, while increasing the α and β rotations. c, Compressive strain induced from the LAO substrate has the opposite effect: increasing the γ rotation, while decreasing the α and β rotations. for LNO on both LAO and STO which indicates excellent accuracy between the two structure determination methods. We note that the DFT ground state indicates an additional energy lowering distortion through small antiparallel displacements of ∼ 0 . 01 ˚ A for the La atoms along the [110] directions. Such displacements would produce weak but measurable ( 1 / 2 1 / 2 1 / 2 ) and ( 3 / 2 3 / 2 3 / 2 ) peaks, which however were not observed in the diffraction measurements, and likely persists in the DFT calculations due to the common exchange-correlation functional underestimation of the equilibrium volume. 8