An accurate and easily extendable method to deal with lattice dynamics of solids is offered. It based on first-principles molecular simulations provides a consistent way extract the best possible harmonic - or higher order potential energy surface at finite temperatures. designed work even for strongly anharmonic systems where traditional quasiharmonic approximation fails. The accuracy convergence are controlled in straightforward way. Excellent agreement calculated phonon dispersion...

We have developed a thorough and accurate method of determining anharmonic free energies, the temperature dependent effective potential technique (TDEP). It is based on ab initio molecular dynamics followed by mapping onto model Hamiltonian that describes lattice dynamics. The formalism numerical aspects are described in detail. A number practical examples given, results presented, which confirm usefulness TDEP within classical frameworks. In particular, we examine from first principles...

The temperature dependent effective potential (TDEP) method is generalized beyond pair interactions. second and third order force constants are determined consistently from ab initio molecular dynamics simulations at finite temperature. reliability of the approach demonstrated by calculations Mode Gr\"uneisen parameters for Si. We show that extension TDEP to higher allows an efficient calculation phonon life time, in Si as well $\epsilon$-FeSi, a system exhibits anomalous softening with

The Temperature Dependent Effective Potential (TDEP) method is a versatile and efficient approach to include temperature in ab initio materials simulations based on phonon theory.TDEP can be used describe thermodynamic properties classical quantum ensembles, several response ranging from thermal transport Neutron Raman spectroscopy.A stable fast reference implementation given the software package of same name described here.The underlying theoretical framework foundation briefly sketched...

We present first-principles calculations of the thermal and transport properties ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ that combine an ab initio molecular dynamics (AIMD) approach to calculate interatomic force constants (IFCs) along with a full iterative solution Peierls-Boltzmann equation for phonons. The newly developed AIMD allows determination harmonic anharmonic forces at each temperature, which is particularly appropriate highly materials such as ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$....

The anharmonic lattice dynamics of rock-salt thermoelectric compounds SnTe and PbTe are investigated with inelastic neutron scattering (INS) first-principles calculations. experiments show that, surprisingly, although is closer to the ferroelectric instability, phonon spectra in exhibit a more character. This behavior reproduced calculations temperature-dependent self-energy. Our simulations reveal how nesting dispersions induces prominent features self-energy, which account for measured INS...

Structural phase transitions and soft phonon modes pose a long-standing challenge to computing electron-phonon (e-ph) interactions in strongly anharmonic crystals. Here we develop first-principles approach compute e-ph scattering charge transport materials with lattice dynamics. Our employs renormalized phonons the temperature-dependent coupling for all modes, including associated ferroelectricity transitions. We show that electron mobility cubic SrTiO_{3} is controlled by longitudinal...

The lead-free halide double perovskite class of materials offers a promising venue for resolving issues related to toxicity Pb and long-term stability the lead-containing perovskites. We present first-principles study lattice vibrations in Cs_{2}AgBiBr_{6}, prototypical compound this show that dynamics Cs_{2}AgBiBr_{6} is highly anharmonic, largely regards tilting AgBr_{6} BiBr_{6} octahedra. Using an energy- temperature-dependent phonon spectral function, we then how experimentally observed...

We investigate the harmonic and anharmonic contributions to phonon spectrum of lead telluride perform a complete characterization how thermal properties PbTe evolve as temperature increases. analyze resistivity's variation with clarify misconceptions about existing experimental literature. The resistivity initially increases sublinearly because phase space effects ultra strong renormalizations specific bands. This effect is strongest factor in favorable thermoelectric PbTe, it explains its...

Lead chalcogenides such as PbS, PbSe, and PbTe are of interest for their exceptional thermoelectric properties strongly anharmonic lattice dynamics. Although has received the most attention, PbSe a lower thermal conductivity despite being stiffer, trend that prior first-principles calculations have not reproduced. Here, we use ab-initio explicitly account strong anharmonicity to identify origin this low an anomalously large interaction, exceeding in strength PbTe, between transverse optic...

The interest in improving the thermoelectric response of bulk materials has received a boost after it been recognized that layered materials, particular SnSe, show very large figure merit. This result great attention while is now possible to conceive other similar or experimental methods improve this value. Before we can think engineering material important understand basic mechanism explains unusual behavior, where low thermal conductivity and high thermopower from delicate balance between...

Despite the widespread use of silicon in modern technology, its peculiar thermal expansion is not well-understood. Adapting harmonic phonons to specific volume at temperature, quasiharmonic approximation, has become accepted for simulating expansion, but given ambiguous interpretations microscopic mechanisms. To test atomistic mechanisms, we performed inelastic neutron scattering experiments from 100-1500K on a single-crystal measure changes phonon frequencies. Our state-of-the-art ab initio...

Abstract The proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ . However, GeTe increases at ferroelectric transition near 700 K. Using first-principles calculations with temperature dependent effective potential method, we show that this rise consequence negative expansion rhombohedral increase lifetimes high-symmetry phase. Strong induces...

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2 AgBiBr6 , has been recently studied as a lead-free alternative for optoelectronic applications. However, does not exhibit excellent activity lead-based perovskites. Therefore, explore correlation between dynamics and properties in perovskites, investigated compared its...

Structural phase transitions in epitaxial stoichiometric $\mathrm{VN}/\mathrm{MgO}(011)$ thin films are investigated using temperature-dependent synchrotron x-ray diffraction (XRD), selected-area electron (SAED), resistivity measurements, high-resolution cross-sectional transmission microscopy, and ab initio molecular dynamics (AIMD). At room temperature, VN has the B1 NaCl structure. However, below ${T}_{c}=250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, XRD SAED results reveal forbidden...

Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. First-principles simulations based on ab initio molecular dynamics (AIMD). Computational efficiency the method is greatly enhanced by careful preparation initial state simulation cell that minimizes or completely removes need for equilibration and therefore allows parallel AIMD calculations. constants ${C}_{11}$, ${C}_{12}$, ${C}_{44}$ calculated. A strong dependence predicted, with ${C}_{11}$...

We develop a method to accurately and efficiently determine the vibrational free energy as function of temperature volume for substitutional alloys from first principles. Taking ${\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{N}$ alloy model system, we calculate isostructural phase diagram by finding global minimum corresponding true equilibrium state system. demonstrate that contribution including anharmonicity dependence mixing enthalpy have decisive impact on calculated alloy,...

Molecular crystals such as polyethylene are of intense interest flexible thermal conductors, yet their intrinsic upper limits conductivity remain unknown. Here, we report a study the vibrational properties and lattice molecular crystal using an ab initio approach that rigorously incorporates nuclear quantum motion finite temperature effects. We obtain along chain direction around $160\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{m}}^{\ensuremath{-}1}\text{ }{\mathrm{K}}^{\ensuremath{-}1}$ at...

Lead chalcogenides have exceptional thermoelectric properties and intriguing anharmonic lattice dynamics underlying their low thermal conductivities. An ideal material for efficiency is the phonon glass-electron crystal, which drives research on strategies to scatter or localize phonons while minimally disrupting electronic-transport. Anharmonicity can potentially do both, even in perfect crystals, simulations suggest that PbSe enough support intrinsic localized modes halt transport. Here,...

The anharmonic lattice dynamics of oxide and halide perovskites play a crucial role in their mechanical optical properties. Raman spectroscopy is one the key methods used to study these structural dynamics. However, despite decades research, existing interpretations cannot explain temperature dependence observed spectra. We demonstrate nonmonotonic evolution with scattering intensity present model for second-order that accounts this unique trend. By invoking low-frequency feature, we are...

Progress in materials science through thermodynamic modelling may rest crucially on access to a database, such as that developed by Scientific Group Thermodata Europe (SGTE) around 1990. It gives the Gibbs energy of elements form series function temperature, i.e. essentially curve fitting experimental data. In light progress theoretical understanding and first‐principles calculation methods, possibility for an improved database description thermodynamics has become evident. is purpose this...

Ti1−xAlxN is a technologically important alloy that undergoes process of high temperature age-hardening strongly influenced by its elastic properties. We have performed first principles calculations the constants and anisotropy using symmetry imposed force constant dependent effective potential method, which include lattice vibrations therefore effects temperature, including thermal expansion intrinsic anharmonicity. These are compared with in situ x-ray diffraction measurements parameter....

Abstract Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge the local silicates silica (SiO 2 ) melts at mantle conditions densification mechanisms is still limited. Here we report synthesis characterization metastable high-pressure phases, coesite-IV coesite-V, using in situ single-crystal X-ray diffraction ab initio simulations. Their crystal are drastically different from any previously considered...

Transition metal dichalcogenides (TMDs) are a class of layered materials that hold great promise for wide range applications. Their practical use can be limited by their thermal transport properties, which have proven challenging to determine accurately, both from theoretical and experimental perspective. We conducted thorough investigation the conductivity four common TMDs, <a:math...