Add kinetic-energy density and variational meta-GGA support for PW, PAW and FP-LAPW

[DCM-Uni-Paderborn]

Summary

Implement positive orbital kinetic-energy density and self-consistent, tau-dependent Libxc meta-GGAs for norm-conserving plane-wave, PAW and FP-LAPW calculations.

This provides the kinetic-energy-density foundation for using Skala in SIRIUS through CP2K. The first follow-up will add reconstructed-field XC callbacks. A further SIRIUS PR will add geometry derivatives, GPU execution and spinor/SOC support.

Implementation

• Generate spin-resolved kinetic-energy density and include it in density mixing and restart storage.
• Add the corresponding generalized Kohn-Sham operators and consistent total-energy and double-counting terms.
• Implement PAW all-electron and pseudo partial-wave contributions with consistent compensation-charge treatment.
• Implement FP-LAPW interstitial and muffin-tin contributions, including augmented waves and local orbitals.
• Support setup-provided core kinetic densities and a variational nonrelativistic radial core solver.
• Connect both exact and Davidson diagonalization.

Validation

Focused tests cover orbital derivatives, energy consistency, core contributions, mixing, restart and serial/MPI execution. Exact and Davidson SCF results agree within approximately 1.1e-8 Ha across the tested PW, PAW and FP-LAPW cases.

Existing FFT, spherical-harmonic and spline tests also pass.

Supported Scope

CPU double-precision calculations with unpolarized or collinear spin and nonhybrid, tau-dependent Libxc functionals. Variational evaluation requires Libxc 7 or newer.

PAW and FP-LAPW currently require disabled symmetry reduction and Lebedev quadrature. FP-LAPW requires nonrelativistic valence and core states. PAW and nonlinear-core-corrected pseudopotentials require the appropriate core kinetic-density data.

Forces, stress, GPU execution, spin-orbit coupling, noncollinear spin and ultrasoft pseudopotentials are not included. Unsupported configurations are rejected explicitly.

Related to #1027.

[simonpintarelli]

cscs-ci run default

[simonpintarelli]

cscs-ci run default