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SUMMARY:In- and out-of-equilibrium ab initio theory of electrons and phono
ns
DTSTART:20231016T120000Z
DTEND:20231016T130000Z
DTSTAMP:20240304T074700Z
UID:indico-event-37636@agenda.infn.it
DESCRIPTION:Speakers: Gianluca Stefanucci (ROMA2)\n\nWe lay down the ab in
itio many-body quantum theory of electrons and phonons in equilibrium as
well as in steady-state or time-varying settings. The focus is on the har
monic approximation\, but the developed tools can readily incorporate anha
rmonic effects. We begin by showing the necessity of determining the ab i
nitio Hamiltonian in a self-consistent manner to ensure the existence of
an equilibrium state. We then identify the correct partitioning into a
“noninteracting” and an “interacting” part to carry out diagramma
tic expansions in terms of dressed propagators and screened interactions.
The final outcome is the finite-temperature nonequilibrium extension of t
he Hedin equations\, showcasing the emergence of the coupling between ele
ctrons and coherent phonons through the time-local Ehrenfest diagram. The
Hedin equations have limited practical utility for real-time simulations
of systems driven out of equilibrium by external fields. We then derive
the Kadanoff-Baym equations for electrons and phonons\, discuss the theor
y of conserving approximations and show how to recover the Born-Oppenheim
er approximation. We conclude by pointing out a possible correlation-indu
ced splitting of the phonon dispersion in materials with no time-reversal
invariance.\n\nhttps://agenda.infn.it/event/37636/
LOCATION:AULA GRASSANO
URL:https://agenda.infn.it/event/37636/
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