9 research outputs found
Calculation of excited polaron states in the Holstein model
An exact diagonalization technique is used to investigate the low-lying
excited polaron states in the Holstein model for the infinite one-dimensional
lattice. For moderate values of the adiabatic ratio, a new and comprehensive
picture, involving three excited (coherent) polaron bands below the phonon
threshold, is obtained. The coherent contribution of the excited states to both
the single-electron spectral density and the optical conductivity is evaluated
and, due to the invariance of the Hamiltonian under the space inversion, the
two are shown to contain complementary information about the single-electron
system at zero temperature. The chosen method reveals the connection between
the excited bands and the renormalized local phonon excitations of the
adiabatic theory, as well as the regime of parameters for which the electron
self-energy has notable non-local contributions. Finally, it is shown that the
hybridization of two polaron states allows a simple description of the ground
and first excited state in the crossover regime.Comment: 12 pages, 9 figures, submitted to PR
Phase diagram of the Holstein polaron in one dimension
The behavior of the 1D Holstein polaron is described, with emphasis on
lattice coarsening effects, by distinguishing between adiabatic and
nonadiabatic contributions to the local correlations and dispersion properties.
The original and unifying systematization of the crossovers between the
different polaron behaviors, usually considered in the literature, is obtained
in terms of quantum to classical, weak coupling to strong coupling, adiabatic
to nonadiabatic, itinerant to self-trapped polarons and large to small
polarons. It is argued that the relationship between various aspects of polaron
states can be specified by five regimes: the weak-coupling regime, the regime
of large adiabatic polarons, the regime of small adiabatic polarons, the regime
of small nonadiabatic (Lang-Firsov) polarons, and the transitory regime of
small pinned polarons for which the adiabatic and nonadiabatic contributions
are inextricably mixed in the polaron dispersion properties. The crossovers
between these five regimes are positioned in the parameter space of the
Holstein Hamiltonian.Comment: 19 pages, 9 figure
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries
Bipolarons and polarons in the Holstein-Hubbard model: analogies and differences
The single bipolaron problem is examined in the context of the 1D Holstein-Hubbard
model, emphasizing analogies and differences with respect to the complementary single
polaron physics. The bipolaron band structure below the phonon threshold is revealed,
showing a complex relationship between numerous excited bands as the adiabatic limit is
approached. Light bipolarons with significant binding energy, the stability of large
bipolarons, the small to large bipolaron crossover as a function of the Hubbard repulsion,
as well as the bipolaron dissociation, are investigated in detail, disentangling
adiabatic, nonadiabatic and lattice coarsening effects. It is emphasized that condensation
of bipolarons occurs in the dilute limit only at very low temperatures
Bipolarons and polarons in the Holstein-Hubbard model: analogies and differences
The single bipolaron problem is examined in the context of the 1D
Holstein-Hubbard model, emphasizing analogies and differences with respect to
the complementary single polaron physics. The bipolaron band structure below
the phonon threshold is revealed, showing a complex relationship between
numerous excited bands as the adiabatic limit is approached. Light bipolarons
with significant binding energy, the stability of large bipolarons, the small
to large bipolaron crossover as a function of the Hubbard repulsion, as well as
the bipolaron dissociation, are investigated in detail, disentangling
adiabatic, nonadiabatic and lattice coarsening effects. It is emphasized that
condensation of bipolarons occurs in the dilute limit only at very low
temperatures.Comment: 12 pages, 7 figure