Excitation energies extended systems

Two-dimensional constant matrix, transition state trajectory, white noise, 203-207 Two-pathway excitation, coherence spectroscopy atomic systems, 170-171 channel phases, 148-149 energy domain, 178-182 extended systems and dissipative environments, 177-185 future research issues, 185-186 isolated resonance, coupled continuum, 168-169... 

The particle density in an isolated bounded system is required to be zero at the boundary point at infinity. This introduces gaps (or discreteness) in the excitation spectrum, at low energy, which are not present in extended systems. The presence of shell structure, and whether the shells are open or closed, is... 

This part introduces variational principles relevant to the quantum mechanics of bound stationary states. Chapter 4 covers well-known variational theory that underlies modern computational methodology for electronic states of atoms and molecules. Extension to condensed matter is deferred until Part III, since continuum theory is part of the formal basis of the multiple scattering theory that has been developed for applications in this subfield. Chapter 5 develops the variational theory that underlies independent-electron models, now widely used to transcend the practical limitations of direct variational methods for large systems. This is extended in Chapter 6 to time-dependent variational theory in the context of independent-electron models, including linear-response theory and its relationship to excitation energies. 

The zeroth-order wavefunction of an excited state in an extended system cannot be described by a single determinant since the energies of the excited determinants form continuous bands. The states associated with the same band are degenerate since the energy difference between two adjacent states is an infinitesimal number. Thus, to calculate the energy spectrum of excited states, one needs to use degenerate MBPT, two-particle green function theory or a method like EOM-CC [5],... 

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