95 research outputs found
Point-Defect Optical Transitions and Thermal Ionization Energies from Quantum Monte Carlo Methods: Application to F-center Defect in MgO
We present an approach to calculation of point defect optical and thermal
ionization energies based on the highly accurate quantum Monte Carlo methods.
The use of an inherently many-body theory that directly treats electron
correlation offers many improvements over the typically-employed density
functional theory Kohn-Sham description. In particular, the use of quantum
Monte Carlo methods can help overcome the band gap problem and obviate the need
for ad-hoc corrections. We demonstrate our approach to the calculation of the
optical and thermal ionization energies of the F-center defect in magnesium
oxide, and obtain excellent agreement with experimental and/or other
high-accuracy computational results
Leveraging Language Representation for Material Recommendation, Ranking, and Exploration
Data-driven approaches for material discovery and design have been
accelerated by emerging efforts in machine learning. While there is enormous
progress towards learning the structure to property relationship of materials,
methods that allow for general representations of crystals to effectively
explore the vast material search space and identify high-performance candidates
remain limited. In this work, we introduce a material discovery framework that
uses natural language embeddings derived from material science-specific
language models as representations of compositional and structural features.
The discovery framework consists of a joint scheme that, given a query
material, first recalls candidates based on representational similarity, and
ranks the candidates based on target properties through multi-task learning.
The contextual knowledge encoded in language representations is found to convey
information about material properties and structures, enabling both similarity
analysis for recall, and multi-task learning to share information for related
properties. By applying the discovery framework to thermoelectric materials, we
demonstrate diversified recommendations of prototype structures and identify
under-studied high-performance material spaces, including halide perovskite,
delafossite-like, and spinel-like structures. By leveraging material language
representations, our framework provides a generalized means for effective
material recommendation, which is task-agnostic and can be applied to various
material systems
Insulator-to-Metal Transition in Selenium-Hyperdoped Silicon: Observation and Origin
Hyperdoping has emerged as a promising method for designing semiconductors
with unique optical and electronic properties, although such properties
currently lack a clear microscopic explanation. Combining computational and
experimental evidence, we probe the origin of sub-band gap optical absorption
and metallicity in Se-hyperdoped Si. We show that sub-band gap absorption
arises from direct defect-to-conduction band transitions rather than free
carrier absorption. Density functional theory predicts the Se-induced
insulator-to-metal transition arises from merging of defect and conduction
bands, at a concentration in excellent agreement with experiment. Quantum Monte
Carlo calculations confirm the critical concentration, demonstrate that
correlation is important to describing the transition accurately, and suggest
that it is a classic impurity-driven Mott transition.Comment: 5 pages, 3 figures (PRL formatted
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