studies of strain accommodation and relaxation in perovskite oxides, allow for more direct comparisons between bulk and thin film materials, and help elucidate the physical mechanisms of novel properties at oxide interfaces. X-ray diffraction measurements were performed at the Advanced Photon Source on Sectors 33-BM and 6-ID using four-circle and six-circle Huber diffractometers. When analyzing the peak intensities, we choose to use the peak height as a measure of intensity. Scans along h and l confirm that the peak widths are independent of their location on the reciprocal lattice. The measured intensity is determined by normalizing for the incident intensity and subtracting background intensity. The calculated intensity is determined using Eqns. (1) and (2). The corrections for the beam footprint, Lorentz polarization factor, and the q dependence of the O 2 − form factor are taken into account in the calculated intensity. The adjustable parameters are the rotation angles, α and γ . In the case of LNO/LAO, we did not attempt to remove any diffuse background from the LAO substrate, which exhibits strong half-order peaks. We estimate the magnitude of this substrate-induced background to be less than 10% of the intensity of the film peak. This value is less than the average agreement between the measured and calculated peak intensities. As such, we do not believe this introduces a significant error into our determination of α and γ . Methods We carry out first-principles density functional theory (DFT) calculations within the local-spin density approximation (LSDA) plus Hubbard U method [28] as implemented in the Vienna ab initio Simulation Package (VASP) [30, 31]. We follow the Dudarev approach [29] and include an effective Hubbard term U$_{eff}$ = U − J of 3 eV to accurately treat the correlated Ni 3 d orbitals. The core and valence electrons are treated with the projector augmented wave (PAW) method [36] with the following valence electron configurations: 5 p $^{6}$5 d $^{1}$6 s 2 (La), 3 p $^{6}$3 d $^{9}$4 s 1 (Ni), and 2 s $^{2}$2 p 4 (O). The Brillouin zone integrations are performed with a Gaussian smearing of 0.05 eV over a 5x5x5 Monkhorst-Pack k -point mesh [37] centered at Γ, and a 450 eV plane-wave cutoff. For structural relaxations we also used a Gaussian broadening technique of 0.05 eV and relaxed the ions until the Hellmann-Feynman forces are less than 1 meV ˚ A − $^{1}$. In all calculations ferromagnetic spin order is enforced, and for our choice of U$_{eff}$ , we accurately reproduce the enhanced paramagnetic spin moment [38]. 11