  We present a combined experimental and computational method which enables the
precise determination of the atomic positions in a thin film using CuK{\alpha}
radiation, only. The capabilities of this technique surpass simple structure
refinement and allow solving unknown phases stabilized by substrate-induced
stress. We derive the appropriate corrections to transform the measured
integrated intensities into structure factors. Data collection was performed
entirely on routinely available laboratory diffractometers (CuK{\alpha}
radiation); the subsequent analysis was carried out by single-crystal direct
methods ({\delta} recycling procedure) followed by the least-squares refinement
of the structural parameters of the unit cell content. We selected an epitaxial
thin film of CuMnAs grown on top of a GaAs substrate, which formed a crystal
structure with tetragonal symmetry, differing from the bulk material which is
orthorhombic. Here we demonstrate the new tetragonal form of epitaxial CuMnAs
grown on GaAs substrate and present consistent high-resolution scanning
transmission electron microscopy and stoichiometry analyses.
