Predicting the thermal conductivity of glasses from first principles has hitherto been a very complex problem.The established Allen-Feldman and Green-Kubo approaches employ approximations with limited validity—the fo...Predicting the thermal conductivity of glasses from first principles has hitherto been a very complex problem.The established Allen-Feldman and Green-Kubo approaches employ approximations with limited validity—the former neglects anharmonicity,the latter misses the quantum Bose-Einstein statistics of vibrations—and require atomistic models that are very challenging for first-principles methods.Here,we present a protocol to determine from first principles the thermal conductivityκ(T)of glasses above the plateau(i.e.,above the temperature-independent region appearing almost without exceptions in theκ(T)of all glasses at cryogenic temperatures).The protocol combines the Wigner formulation of thermal transport with convergence-acceleration techniques,and accounts comprehensively for the effects of structural disorder,anharmonicity,and Bose-Einstein statistics.We validate this approach in vitreous silica,showing that models containing less than 200 atoms can already reproduceκ(T)in the macroscopic limit.We discuss the effects of anharmonicity and the mechanisms determining the trend ofκ(T)at high temperature,reproducing experiments at temperatures where radiative effects remain negligible.展开更多
Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic...Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic local dipoles,a highly nonlocal electronic polarisation can be foreseen in conjugated polymers,characterised by delocalised and highly responsiveπ-electrons.These 1D systems represent a physical realisation of a Thouless pump,a mechanism of adiabatic charge transport of a topological nature which results,as shown in this work,in anomalously large dynamical effective charges,inversely proportional to the bandgap energy.展开更多
Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacu...Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacutingaite,of recent experimental realization,as prototypical systems where the infrared spectrum is discontinuous across the transition,due to sudden and large discretized jumps of the Born effective charges(up to~2).Our results,rationalized thanks to the lowenergy Kane–Mele model,are robust with respect to dynamical effects,relevant when the electronic energy gap is comparable with the phonon frequency.In the small gap QSHI germanene,due to dynamical effects,the in-plane phonon resonance in the optical conductivity shows a Fano profile with remarkable differences in the intensity and the shape between different phases.Instead,the large-gap QSHI jacutingaite presents several IR-active phonon modes whose spectral intensities drastically change between different phases.展开更多
基金N.M.acknowledges funding from the Swiss National Science Foundation under the Sinergia grant no.189924M.S.acknowledges support from Gonville and Caius College,and from the SNSF project P500PT_203178Part of the calculations presented in this work have been performed using computational resources provided by the Cambridge Tier-2 system operated by the University of Cambridge Research Computing Service(www.hpc.cam.ac.uk)funded by EPSRC Tier-2 capital grant EP/T022159/1.
文摘Predicting the thermal conductivity of glasses from first principles has hitherto been a very complex problem.The established Allen-Feldman and Green-Kubo approaches employ approximations with limited validity—the former neglects anharmonicity,the latter misses the quantum Bose-Einstein statistics of vibrations—and require atomistic models that are very challenging for first-principles methods.Here,we present a protocol to determine from first principles the thermal conductivityκ(T)of glasses above the plateau(i.e.,above the temperature-independent region appearing almost without exceptions in theκ(T)of all glasses at cryogenic temperatures).The protocol combines the Wigner formulation of thermal transport with convergence-acceleration techniques,and accounts comprehensively for the effects of structural disorder,anharmonicity,and Bose-Einstein statistics.We validate this approach in vitreous silica,showing that models containing less than 200 atoms can already reproduceκ(T)in the macroscopic limit.We discuss the effects of anharmonicity and the mechanisms determining the trend ofκ(T)at high temperature,reproducing experiments at temperatures where radiative effects remain negligible.
基金The authors acknowledge financial support from the European Union under ERC-SYN MORE-TEM,No.951215from the Italian MIUR through the PRIN-2017 project,Grant No.2017Z8TS5BCINECA awards under ISCRA initiative Grant No.HP10CCJFWR and HP10C7XPLJ for the availability of high-performance computing resources and support.
文摘Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic local dipoles,a highly nonlocal electronic polarisation can be foreseen in conjugated polymers,characterised by delocalised and highly responsiveπ-electrons.These 1D systems represent a physical realisation of a Thouless pump,a mechanism of adiabatic charge transport of a topological nature which results,as shown in this work,in anomalously large dynamical effective charges,inversely proportional to the bandgap energy.
文摘Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacutingaite,of recent experimental realization,as prototypical systems where the infrared spectrum is discontinuous across the transition,due to sudden and large discretized jumps of the Born effective charges(up to~2).Our results,rationalized thanks to the lowenergy Kane–Mele model,are robust with respect to dynamical effects,relevant when the electronic energy gap is comparable with the phonon frequency.In the small gap QSHI germanene,due to dynamical effects,the in-plane phonon resonance in the optical conductivity shows a Fano profile with remarkable differences in the intensity and the shape between different phases.Instead,the large-gap QSHI jacutingaite presents several IR-active phonon modes whose spectral intensities drastically change between different phases.
