Analytic treatment of a polaron in a nonparabolic conduction band

This dataset contains numerical results used to generate selected figures in the manuscript: “Extending the Feynman variational principle and analytical methods to lattice polarons”S. N. Klimin, J. Tempere, M. Houtput, I. Zappacosta, S. Ragni, T. Hahn, L. Celiberti, C. Franchini, and A. S. Mishchenko (2026), accepted in Physical Review B. The data correspond exclusively to calculations performed in the present work.Numerical data taken from previous publications are not included. The archive contains ground-state energies and momentum-dependent polaron dispersions obtained using: * Modified Feynman variational method (full and reduced)* Canonical transformation approach* Improved and standard Wigner-Brillouin approximations* Diagrammatic Monte Carlo (present work) Each data file includes detailed ASCII headers specifying parameters and column definitions. The corresponding figure numbers and computational methods are specified both in the filenames and in the header comments within each data file.