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First-principles thermal equation of state of fcc iridium
Kai Luo, Ruifeng Lu, R. E. Cohen
The thermal equation of states for fcc iridium (Ir) is obtained from first-principles molecular dynamics up to 3000 K and 540 GPa. The equation of state (EoS) is globally fitted to…
First-principles Calculations of Raman and Infrared Spectroscopy For Phase Identification and Strain Calibration of Hafnia
Aldo Raeliarijaona, R. E. Cohen
Using density functional perturbation theory (DFPT) we computed the phonon frequencies, Raman and IR activities of hafnia polymorphs (P4nmc, Pca2, Pmn2, Pbca OI,…
Stable Polar Oxynitrides through Epitaxial Strain
Li Zhu, Hiroyuki Takenaka, R. E. Cohen
We investigate energetically favorable structures of ABON oxynitrides as functions of pressure and strain via swarm-intelligence-based structure prediction methods, DFT lattice…
Prediction of an Extended Ferroelectric Clathrate
Li Zhu, Timothy A. Strobel, R. E. Cohen
Using first-principles calculations, we predict a lightweight room-temperature ferroelectric carbon-boron framework in a host/guest clathrate structure. This ferroelectric clathrat…
Giant electrocaloric effect at the antiferroelectric-to-ferroelectric phase boundary in PbZrTiO
A. V. Kimmel, O. T. Gindele, D. M. Duffy +1
Molecular dynamics simulations predict a giant electrocaloric effect at the ferroelectric-antiferroelectric phase boundary in PZT (PbTiO-PbZrO). These large-scale simulatio…
Towards a systematically improvable many-body description of antiferromagnetic iron oxide
Joshua P Townsend, Raymond C Clay, Thomas R Mattsson +5
We report variational and fixed-node diffusion quantum Monte Carlo (QMC) calculations of anti-ferromagnetic iron oxide (FeO) in the ground state B1 crystal structure. The goal of t…
Valence and Spin fluctuations in Mn-doped ferroelectric BaTiO3
Subhasish Mandal, R. E. Cohen, K. Haule
We study Mn substitution for Ti in BaTiO3 with and without compensating oxygen vacancies using density functional theory (DFT) in combination with dynamical mean field theory (DMFT…
Polarization rotation and the electrocaloric effect in barium titanate
H. H. Wu, R. E. Cohen
We study the electrocaloric effect in the classic ferroelectric BaTiO3 through a series of phase transitions driven by applied electric field and temperature. We find both negative…
Thermal conductivity and electrical resistivity of solid iron at Earth's core conditions from first-principles
Junqing Xu, Peng Zhang, K. Haule +4
We compute the thermal conductivity and electrical resistivity of solid hcp Fe to pressures and temperatures of Earth's core. We find significant contributions from electron-electr…
Effect of aging and Mn substitution on anisotropy of third generation piezoelectrics
Rajasekarakumar Vadapoo, Muhtar Ahart, Margo Staruch +4
We predict a new candidate high-temperature high-pressure structure of FeSiO with space-group symmetry Cmmm by applying an evolutionary algorithm within DFT+U that we call post…
Electric field induced phase transition and electrocaloric effect in PMN-PT
H. H. Wu, R. E. Cohen
Ferroelectric perovskite oxides possess a large electrocaloric (EC) effect, but usually at high temperatures near the ferroelectric/paraelectric phase transition temperature, which…
Stable Charged Antiparallel Domain Walls in Hyperferroelectrics
Shi Liu, R. E. Cohen
Charge-neutral 180 domain walls that separate domains of antiparallel polarization directions are common structural topological defects in ferroelectrics. In normal ferroel…
Multiscale Simulations of Defect Dipole-Enhanced Electromechanical Coupling at Dilute Defect Concentrations
Shi Liu, R. E. Cohen
The role of defects in solids of mixed ionic-covalent bonds such as ferroelectric oxides is complex. Current understanding of defects on ferroelectric properties at the single-defe…
Structural Diversity in Lithium Carbides
Yangzheng Lin, Timothy A. Strobel, R. E. Cohen
The lithium-carbon binary system possesses a broad range of chemical compounds, which exhibit fascinating chemical bonding characteristics that give rise diverse and technologicall…
Caloric Effects in Methylammonium Lead Iodide from Molecular Dynamics Simulations
Shi Liu, Ronald E. Cohen
Organic-inorganic hybrid perovskite architecture could serve as a robust platform for materials design to realize functionalities beyond photovoltaic applications. We explore calor…
Effects of Manganese Addition on the Electronic Structure of BaTiO
J. F. Nossa, Ivan I. Naumov, R. E. Cohen
Mn is used as a dopant to improve the electromechanical properties of perovskite oxides. We elucidate the role of Mn defects and associated vacancies on the electronic, atomic and…
First principles based atomistic modeling of phase stability in PMN-xPT
M. Sepliarsky, R. E. Cohen
We have performed molecular dynamics simulations using a shell model potential developed by fitting first principles results to describe the behavior of the relaxor-ferroelectric (…
Orbital ordering, ferroelasticity, and the large pressure induced volume collapse in PbCrO3
P. Ganesh, R. E. Cohen
We report a new tetragonal ground-state for perovskite-structured PbCrO3 from DFT+U calculations, and explain its anomalously large volume. The new structure is stabilized due to o…
Anomalous optical and electronic properties of dense sodium
Dafang Li, Hanyu Liu, Bao-Tian Wang +4
Based on ab initio density-functional-theory using generalized gradient approximation, we systematically study the optical and electronic properties of the insulating dense sodium…
Quantum Monte Carlo for minerals at high pressure: Phase stability, equations of state, and elasticity of silica
K. P. Driver, R. E. Cohen, Zhigang Wu +5
Silica is an abundant component of the Earth whose crystalline polymorphs play key roles in its structure and dynamics. As the simplest silicates, understanding pure silica is a pr…
First principle based phase stability in PMN-xPT
M. Sepliarsky, R. E. Cohen
We have applied a shell model potential developed by fitting first principle results to describe the behavior of the relaxor-ferroelectric PMN-xPT as function of concentration. The…
Prediction of polar ordered oxynitride perovskites
Razvan Caracas, R. E. Cohen
Using a materials by design approach, the authors find a class of ordered oxynitride piezoelectrics with perovskite structure. They predict that ordered YSiO2N and YGeO2N are chara…
First Principles Theories of Piezoelectric Materials
R. E. Cohen
Piezoelectrics have long been studied using parameterized models fit to experimental data, starting with the work of Devonshire in 1954. Much has been learned using such approaches…
Brillouin scattering and molecular dynamics study of the elastic properties of Pb(Mg1/3Nb2/3)O3
Muhtar Ahart, Aravind Asthagiri, Zuo-Guang Ye +4
We report the complete set of elastic constants and the bulk modulus for single crystal Pb(Mg1/3Nb2/3)O3 (PMN) at room temperature obtained from Brillouin spectroscopy and molecula…