The kp method, combined with group theory, is an efficient approach to obtain the low energy effective Hamiltonians of crystalline materials. Although the Hamiltonian coefficients are written as matrix elements of the generalized momentum operator π = p + pSOC (including spin-orbit coupling corrections), their numerical values must be determined from outside sources, such as experiments or ab initio methods. In Ref. [1], we develop a code to explicitly calculate the Kane (linear in crystal momentum) and Luttinger (quadratic in crystal momentum) parameters of kp effective Hamiltonians directly from ab initio wavefunctions provided by Quantum ESPRESSO. Additionally, the code analyzes the symmetry transformations of the wavefunctions to optimize the final Hamiltonian. This is an optional step in the code, where it numerically finds the unitary transformation U that rotates the basis towards an optimal symmetry-adapted representation informed by the user. In this talk, we present the methodology in detail and illustrate the capabilities of the code applying it to a selection of relevant materials. Particularly, we show a "hands-on" example of how to run the code for graphene (with and without spin-orbit coupling), results for the effective parameters for seminal materials, like GaAs. We'll finish the talk point towards the next steps in hte code development.

The code is open source and available at https://gitlab.com/dft2kp/dft2kp. We acknowledge funding from CNPQ, CAPES and FAPEMIG.

[1] J. V. V. Cassiano, A. L. Araújo, P. E. Faria Junior, G. J. Ferreira, SciPost Phys. Codebases 25 (2024)