Spin refactor

[AvirupSircar]

Spin-Polarized DFT Refactor Using MultiVectorProductSpace

• New MultiVectorProductSpace and MultiVectorProductSpaceBlocked abstractions (linearAlgebra/)

  • Introduced two new wavefunction container classes with a flat M × S × N layout (DOFs × spin spaces × orbitals).
  • MultiVectorProductSpaceBlocked is a type-tag subclass that dispatches collinear spin computations to per-spin-space blocked implementations in eigensolvers and orthonormalization routines.
  • MultiVectorProductSpace handles the coupled non-collinear case, where the two spin components are stored in an interleaved product-space representation.

• New MultiVectorOps utility library (linearAlgebra/MultiVectorOps.h/.t.cpp)

  • Added a collection of spin-aware multi-vector operations for product-space wavefunctions, including:
    • Orthonormalization
    • Rayleigh–Ritz projection and diagonalization
    • Chebyshev filtering
  • Provides a common interface for both collinear and non-collinear spin calculations.

• Extended KohnShamDFT constructors

  • Added support for a SpinMode enumeration:
    • Unpolarized
    • Collinear
    • NonCollinear
  • Added per-atom magnetic Z-factors (atomMagZFactors) for constructing the initial collinear magnetization guess.
  • Wavefunction allocation and initialization now branch dynamically based on the selected spin mode.

• New HamiltonianSpinBlockCopyKernels (ksdft/)

  • Introduced CPU/GPU kernels for assembling K spin-block submatrices into the full S·DOF × S·DOF Hamiltonian.
  • Supports both:
    • DOF-fastest storage layout
    • Spin-fastest storage layout

• Spin-aware eigensolvers and Hamiltonian operators

  • Updated the following components to operate with the new product-space wavefunction interface and correctly dispatch spin-channel operations:
    • RayleighRitzEigenSolver
    • OrthonormalizationFunctions
    • ChebyshevFilteredEigenSolver
    • DensityCalculator
    • KineticFE
    • ExchangeCorrelationFE
    • ElectrostaticLocalFE
    • ElectrostaticONCVNonLocFE
  • Added spin-channel indexing and runtime dispatch for both collinear and non-collinear calculations throughout the Kohn–Sham DFT workflow.