16 research outputs found
Ab initio calculations of third-order elastic coefficients
Third-order elasticity (TOE) theory is predictive of strain-induced changes
in second-order elastic coefficients (SOECs) and can model elastic wave
propagation in stressed media. Although third-order elastic tensors have been
determined based on first principles in previous studies, their current
definition is based on an expansion of thermodynamic energy in terms of the
Lagrangian strain near the natural, or zero pressure, reference state. This
definition is inconvenient for predictions of SOECs under significant initial
stresses. Therefore, when TOE theory is necessary to study the strain
dependence of elasticity, the seismological community has resorted to an
empirical version of the theory.
This study reviews the thermodynamic definition of the third-order elastic
tensor and proposes using an "effective" third-order elastic tensor. We extend
the ab initio approach to calculate third-order elastic tensors under finite
pressure and apply it to two cubic systems, namely, NaCl and MgO. As
applications and validations, we evaluate (a) strain-induced changes in SOECs
and (b) pressure derivatives of SOECs based on ab initio calculations. Good
agreement between third-order elasticity-based predictions and numerically
calculated values confirms the validity of our theory
High throughput sampling of phase space with deep learning potentials: -AlOOH at geophysical conditions
Hydrous and nominally anhydrous minerals (NAMs) are a fundamental class of
solids of enormous significance to geophysics. They are the water carriers in
the deep geological water cycle. They impact structural, elastic, plastic, and
thermodynamic properties and phase relations in Earth's forming aggregates
(rocks). They play a critical role in the geochemical and geophysical processes
that shape the planet. Their complexity has prevented predictive calculations
of their properties, but progress in materials simulations ushered by machine
learning potentials is transforming this state of affairs. Here, we adopt a
hybrid approach that combines deep learning potentials (DP) with the SCAN
meta-GGA functional to simulate a prototypical hydrous system. We illustrate
the viability, success, and necessity of this approach to simulate
-AlOOH (), a phase capable of transporting water down to near
the core-mantle boundary of the Earth (~2,900 km depth and ~135 GPa) in
subducting slabs. High-throughput sampling of phase space using molecular
dynamics simulations with DP-potentials offers a panoramic view of the
hydrogen-bond behavior and proton diffusion at geophysical conditions. These
simulations provide a pathway for a deeper understanding of these crucial
components that shape Earth's internal state
Ab initio study on the stability and elasticity of brucite
Brucite (Mg(OH)) is a mineral of great interest owing to its various
applications and roles in geological processes. Its structure, behavior under
different conditions, and unique properties have been the subject of numerous
studies and persistent debate. As a stable hydrous phase in subduction zones,
its elastic anisotropy can significantly contribute to the seismological
properties of these regions. We performed ab initio calculations to investigate
brucite's stability, elasticity, and acoustic velocities. We tested several
exchange-correlation functionals and managed to obtain stable phonons for the
P phase with rSCAN for the first time at all relevant pressures up
to the mantle transition zone. We show that rSCAN performs very well in
brucite, reproducing the experimental equation of state and several key
structure parameters related to hydrogen positions. The room temperature
elasticity results in P reproduces the experimental results at ambient
pressure. These results, together with the stable phonon dispersion of
P at all relevant pressures, indicate P is the stable
candidate phase not only at elevated pressures but also at ambient conditions.
The success of rSCAN in brucite, suggests this functional should be
suitable for other challenging layer-structured minerals, e.g., serpentines, of
great geophysical significance
Thermoelastic properties of bridgmanite using Deep Potential Molecular Dynamics
MgSiO_3-perovskite (MgPv) plays a crucial role in the Earth's lower mantle.
This study combines deep-learning potential (DP) with density functional theory
(DFT) to investigate the structural and elastic properties of MgPv under lower
mantle conditions. To simulate complex systems, we developed a series of
potentials capable of faithfully reproducing DFT calculations using different
functionals, such as LDA, PBE, PBEsol, and SCAN meta-GGA functionals. The
obtained predictions exhibit remarkable reliability and consistency, closely
resembling experimental measurements. Our results highlight the superior
performance of the DP-SCAN and DP-LDA in accurately predicting high-temperature
equations of states and elastic properties. This hybrid computational approach
offers a solution to the accuracy-efficiency dilemma in obtaining precise
elastic properties at high pressure and temperature conditions for minerals
like MgPv, which opens a new way to study the Earth's interior state and
related processes
Elastic anisotropy of lizardite at subduction zone conditions
Subduction zones transport water into Earth's deep interior through slab
subduction. Serpentine minerals, the primary hydration product of ultramafic
peridotite, are abundant in most subduction zones. Characterization of their
high-temperature elasticity, particularly their anisotropy, will help us better
estimate the extent of mantle serpentinization and the Earth's deep water
cycle. Lizardite, the low-temperature polymorph of serpentine, is stable under
the P-T conditions of cold subduction slabs (< 260{\deg}C at 2 GPa), and its
high-temperature elasticity remains unknown. Here we report ab initio
elasticity and acoustic wave velocities of lizardite at P-T conditions of
subduction zones. Our static results agree with previous studies. Its
high-temperature velocities are much higher than previous experimental-based
lizardite estimates with chrysotile but closer to antigorite velocities. The
elastic anisotropy of lizardite is much larger than that of antigorite and
could better account for the observed large shear-wave splitting in some cold
slabs such as Tonga
DeePMD-kit v2: A software package for Deep Potential models
DeePMD-kit is a powerful open-source software package that facilitates
molecular dynamics simulations using machine learning potentials (MLP) known as
Deep Potential (DP) models. This package, which was released in 2017, has been
widely used in the fields of physics, chemistry, biology, and material science
for studying atomistic systems. The current version of DeePMD-kit offers
numerous advanced features such as DeepPot-SE, attention-based and hybrid
descriptors, the ability to fit tensile properties, type embedding, model
deviation, Deep Potential - Range Correction (DPRc), Deep Potential Long Range
(DPLR), GPU support for customized operators, model compression, non-von
Neumann molecular dynamics (NVNMD), and improved usability, including
documentation, compiled binary packages, graphical user interfaces (GUI), and
application programming interfaces (API). This article presents an overview of
the current major version of the DeePMD-kit package, highlighting its features
and technical details. Additionally, the article benchmarks the accuracy and
efficiency of different models and discusses ongoing developments.Comment: 51 pages, 2 figure
Probing the state of hydrogen in δ-AlOOH at mantle conditions with machine learning potential
Hydrous and nominally anhydrous minerals are a fundamental class of solids of enormous significance to geophysics. They are the water carriers in the deep geological water cycle and impact structural, elastic, plastic, and thermodynamic properties and phase relations in Earth's forming aggregates (rocks). They play a critical role in the geochemical and geophysical processes that shape the planet. Their complexity has prevented predictive calculations of their properties, but progress in materials simulations ushered by machine-learning potentials is transforming this state of affairs. Here, we adopt a hybrid approach that combines deep learning potentials (DPs) with the strongly constrained and appropriately normed meta-generalized gradient approximation functional to simulate a prototypical hydrous system. We illustrate the success of this approach to simulate δ-AlOOH (δ), a phase capable of transporting water down to near the core-mantle boundary of the Earth (∼2900km depth and ∼135GPa) in subducting slabs. A high-throughput sampling of phase space using molecular dynamics simulations with DPs sheds light on the hydrogen-bond behavior and proton diffusion at geophysical conditions. These simulations provide a pathway for a deeper understanding of these crucial components that shape Earth's internal state
Ab initio investigation of H-bond disordering in δ-AlOOH
δ-AlOOH (δ) is a high-pressure hydrous phase that participates in the deep geological water cycle. At 0 GPa, δ has asymmetric hydrogen bonds (H bonds). Under pressure, it exhibits H-bond disordering, tunneling, and finally, H-bond symmetrization at ∼18 GPa. This study investigates these 300 K pressure-induced state changes in δ with ab initio calculations. H-bond disordering in δ was modeled using supercell multiconfiguration quasiharmonic calculations. We examine (a) energy barriers for proton jumps, (b) the pressure dependence of phonon frequencies, (c) 300 K compressibility, (d) neutron diffraction pattern anomalies, and (e) compare ab initio bond lengths with measured ones. Such thorough and systematic comparisons indicate that (a) proton “disorder” has a restricted meaning when applied to δ. Nevertheless, H bonds are disordered between 0 and 8 GPa, and a gradual change in H-bond configuration results in enhanced compressibility. (b) Several structural and vibrational anomalies at ∼8 GPa are consistent with the disappearance of a particular (HOC-12) H-bond configuration and its change into another one (HOC-11*). (c) Between 8 and 11 GPa, H-bond configuration (HOC-11*) is generally ordered, at least in short- to midrange scale. (d) Between 11.5 and 18 GPa, H-bond lengths approach a critical value that impedes compression, resulting in decreased compressibility. In this pressure range, especially approaching H-bond symmetrization at ∼18 GPa, anharmonicity and tunneling should play an essential role in the proton dynamics. Further simulations accounting for these effects are desirable to clarify the protons' state in this pressure range
Synthesis, Activity, and Application of Fluorescent Analogs of [D1G, Δ14Q]LvIC Targeting α6β4 Nicotinic Acetylcholine Receptor
α6β4* nicotinic acetylcholine receptor (nAChR)
(* represents
the possible presence of additional subunits) is mainly distributed
in the central and peripheral nervous system and is associated with
neurological diseases, such as neuropathic pain; however, the ability
to explore its function and distribution is limited due to the lack
of pharmacological tools. As one of the analogs of α-conotoxin
(α-CTx) LvIC from Conus lividus, [D1G, Δ14Q]LvIC (Lv) selectively and potently blocks α6/α3β4
nAChR (α6/α3 represents a chimera). Here, we synthesized
three fluorescent analogs of Lv by connecting fluorescent molecules
6-carboxytetramethylrhodamine succinimidyl ester (6-TAMRA-SE, R),
Cy3 NHS ester (Cy3, C) and BODIPY-FL NHS ester (BDP, B) to the N-terminus
of the peptide and obtained Lv-R, Lv-C, and Lv-B, respectively. The
potency and selectivity of three fluorescent peptides were evaluated
using two-electrode voltage-clamp recording on nAChR subtypes expressed
in Xenopus laevis oocytes, and the
potency and selectivity of Lv-B were almost maintained with the half-maximal
inhibition (IC50) of 64 nM. Then, we explored the stability
of Lv-B in artificial cerebrospinal fluid and stained rat brain slices
with Lv-B. The results indicated that the stability of Lv-B was slightly
improved compared to that of native Lv. Additionally, we detected
the distribution of the α6β4* nAChR subtype in the cerebral
cortex using green fluorescently labeled peptide and fluorescence
microscopy. Our findings not only provide a visualized pharmacological
tool for exploring the distribution of the α6β4* nAChR
subtype in various situ tissues and organs but also extend the application
of α-CTx [D1G, Δ14Q]LvIC to demonstrate the involvement
of α6β4 nAChR function in pathophysiology and pharmacology