fixed.hpp

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#pragma once
 
/**
 * FixedOccupation — step-function occupation for insulating systems.
 *
 * All states below the Fermi energy are fully occupied (f=1), all above
 * are empty (f=0). No smearing entropy contribution.
 */
 
#include "layer_4_computation/iterator/internal/smearing/init.hpp"
 
namespace q3 {
 
/// Fixed occupations (insulators): step function.
class FixedOccupation : public SmearingScheme {
  public:
    FixedOccupation() : SmearingScheme(0.0) {}
 
    [[nodiscard]] Real occupation(Real x) const override {
        return x < 0.0 ? 1.0 : 0.0;
    }
    [[nodiscard]] Real entropy_weight(Real /* unused */) const override {
        return 0.0;
    }
    [[nodiscard]] std::string name() const override {
        return "fixed";
    }
};
 
} // namespace q3