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Predicting Thermal Transport in Bi2Te3: From Bulk to Nanostructures Bo Qiu1 and Xiulin Ruan1 1 School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University West Lafayette, IN 47906, U.S.A. ABSTRACT Two-body interatomic potentials in the Morse potential form have been developed for bismuth telluride, and the potentials are used in molecular dynamics (MD) simulations to predict the thermal conductivity of Bi2Te3 bulk, nanowires and few-quintuple thin films. The density functional theory with local density approximations is first used to calculate the total energies for many artificially distorted Bi2Te3 configurations to produce the energy surface. Then by fitting to this energy surface and other experimental data, the Morse potential form is parameterized. Molecular dynamics simulations are then performed to predict the thermal conductivity of bulk Bi2Te3 at different temperatures, and the results agree with experimental data well. We also predicted the thermal conductivity of Bi2Te3 nanowires with diameter ranging from 3 to 30 nm with both smooth (SMNW) and rough (STNW) surfaces. It is found that when the nanowire diameter decreases to the molecular scale (below 10 nm, or the so called "quantum wire"), the thermal conductivity shows significant reduction as compared to bulk value. We find the dimensional crossover behavior of thermal transport in few quintuple layer (QL) thin films at room temperature, and we attribute it to the interplay between phonon Umklapp scattering and boundary scattering. Also, nanoporous films show significantly reduced thermal conductivity compared to perfect thin films, indicating that they can be very promising thermoelectric materials. INTRODUCTION Bi2Te3 as well as its alloys have long been the best thermoelectric material around room temperature with a figure of merit ZT about unity [1-4]. In the last decade, significant enhancement of ZT has been obtained in Bi2Te3 based nanostructures mainly due to the reduced thermal conductivity. Among various nanostructures, Bi2Te3 nanowires and thin films are expected to have reduced thermal conductivity and enhanced ZT as well, and extensive work has been done [5-8]. Reduced To whom correspondence should be addressed thermal conductivity has been seen in these experiments, but enhanced ZT is still yet to be found, indicating that the Seebeck coefficient and/or electrical conductivity have been deteriorated more. For the quasi-2D systems of few-quintuple films, unusual thermal transport phenomena may arise, such as the dimensional crossover behavior seen in few-layer-graphene (FLG) [9]. Also, Bi2Te3 has recently been identified as one of a new class of materials named topological insulators [10], opening a completely new mechanism for Bi2Te3 nanostructures such as the few-quintuple Bi2Te3 thin films to be promising thermoelectric materials. In this work, we use molecular dynamics simulations to predict the lattice thermal conductivity of Bi2Te3 bulk, smooth and rough nanowires with diameter ranging from 3 to 30 nm, as well