Two-temperature warm dense hydrogen as a test of quantum protons driven by orbital-free density functional theory electronic forces

We consider a steady-state(but transient)situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature T_(e),ions at T_(i),and T_(e)≠T_(i).Such states are achievable by pump–probe experiments.For warm dense hydrogen in such a twotemperature situation,we investigate nuclear quantum effects(NQEs)on structure and thermodynamic properties,thereby delineating the limitations of ordinary ab initio molecular dynamics.We use path integral molecular dynamics(PIMD)simulations driven by orbital-free density functional theory(OFDFT)calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence.We calibrate the OFDFT calculations against conventional(explicit orbitals)Kohn–Sham DFT.We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30,the ionic radial distribution function is meaningfully affected by the inclusion of NQEs.Moreover,NQEs induce a substantial increase in both the ionic and electronic pressures.This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen.For Te>20 kK,increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered.In addition,we confirm that compared with thermostatted ring-polymer molecular dynamics,the primitive PIMD algorithm overestimates electronic pressures,a consequence of the overly localized ionic description from the primitive scheme.

Raman spectroscopic identification of normal and malignant human stomach cells

Micro-Raman spectroscopy is employed to identify the normal and malignant human stomach cells. For the cancer cell, the reduced intensity of the Raman peak at 1250 cm^-1 indicates that the protein secondary structure transforms from β-sheet or disordered structures to α-helical, while the increased intensity of the symmetric PO2 stretching vibration mode at 1094 cm^-1 shows the increased DNA content. The ratio of the intensity at 1315 cm^-1 to that at 1340^-1 reduces from 1.8 for the normal cell to 1.1 for the cancer cell in the course of canceration, and the ratio of the intensity at 1655 cm^-1 to that at 1450cm^-1 increases from 1.00 for the cancer cell to 1.26 for the normal cell which indicates that the canceration of stomach cell may induce saturation of the lipid chain.

Magnetovolume and chemical bonding effects of Ni atom in γ'-(Fe_1-xNi_x)_4N compounds

By X-ray diffraction and high pressure Mossbauer spectroscopy, the structure and the hyperfine parameters of Ni substituted γ-Fe4N were investigated. The results of X-ray diffraction indicate that single phase γ’-(Fe1-xNix)4N compounds can be prepared in the composition range of 0≤x≤0.6, and with the increase of Ni content the lattice parameter is fit for the relationship a0(x) = 3.790 5-0.021 57x-0.031 67x2. By high pressure Mossbauer spectra, effects of magnetovolume and chemical bonding of Ni atom on hyperfine magnetic field and isomer shift of iron were distinguished for the first time, and their composition dependences for different lattice sites were studied simultaneously. It is found that the magnetovolume and chemical bonding have different influences on the properties of γ’-(Fe1-xNix)4N, and the latter one plays a key role in the property changes of γ-(Fe1-xNix)4N.

Dependence of surface-enhanced Raman scattering from Calf thymus DNA on anions

Dependence of surface-enhanced Raman scattering （SERS） from Calf thymus DNA on anions is investigated. With the silver colloid, the bands at 732, 960 and 1333 cm^-1 for adenine （A）, 1466 cm^-1 for deoxyribose, and 1652 cm^-1 for the C=O group of thymine （T） are observably enhanced. With the presence of the Cl^- or SO4^2- anions, the bands at 732 and 1326/1329 cm^-1 for the symmetric stretching and skeletal vibrational modes of adenine （A） are dramatically enhanced, and the enhancement effect with the SO4^2- ion is more than that with the Cl^- ion. The experimental results show that the DNA molecule can be adsorbed on the silver colloid particles through the C6N and N7 of adenine （A） the C=O of thymine （T） and deoxyribose. Moreover, the formed hydrogen bonding of the Cl^- or SO4^2- ions to the C6NH2 group of adenine （A） can induce larger C6N electronegativity, which is favor for the C6N/N7 cooperative adsorption on the （Ag）^＋ colloid particles.

Discovery of higher-order topological insulators using the spin Hall conductivity as a topology signature

The discovery and realization of topological insulators,a phase of matter which hosts metallic boundary states when the ddimension insulating bulk is confined to(d−1)-dimensions,led to several potential applications.Recently,it was shown that protected topological states can manifest in(d−2)-dimensions,such as hinge and corner states for three-and two-dimensional systems,respectively.These nontrivial materials are named higher-order topological insulators(HOTIs).Here we show a connection between spin Hall effect and HOTIs using a combination of ab initio calculations and tight-binding modeling.The model demonstrates how a non-zero bulk midgap spin Hall conductivity(SHC)emerges within the HOTI phase.Following this,we performed high-throughput density functional theory calculations to find unknown HOTIs,using the SHC as a criterion.We calculated the SHC of 693 insulators resulting in seven stable two-dimensional HOTIs.Our work guides novel experimental and theoretical advances towards higher-order topological insulator realization and applications.

Discriminating High-Pressure Water Phases Using Rare-Event Determined Ionic Dynamical Properties

Recent discoveries of dynamic ice Ⅶ and superionic ice highlight the importance of ionic diffusions in discriminating high-pressure(P) water phases.The rare event nature and the chemical bond breaking associated with these diffusions,however,make extensive simulations of these processes unpractical to ab initio and inappropriate for force field based methods.Using a first-principles neural network potential,we performed a theoretical study of water at 5-70 GPa and 300-3000 K.Long-time dynamics of protons and oxygens were found indispensable in discriminating several subtle states of water,characterized by proton’s and oxygen ion’s diffusion coefficients and the distribution of proton’s displacements.Within dynamic ice Ⅶ,two types of proton transfer mechanisms,i.e.,translational and rotational transfers,were identified to discriminate this region further into dynamic ice Ⅶ T and dynamic ice Ⅶ R.The triple point between ice Ⅶ,superlonic ice(SI),and liquid exists because the loosening of the bee oxygen skeleton is prevented by the decrease of interatomic distances at high P’s.The melting of ice Ⅶ above ~40 GPa can be understood as a process of two individual steps:the melting of protons and the retarded melting of oxygens,responsible for the forming of SI.The boundary of the dynamic ice VIF and SI lies on the continuation line ice Ⅶ’s melting curve at low P’s.Based on these,a detailed phase diagram is given,which may shed light on studies of water under P’s in a wide range of interdisciplinary sciences.

Autonomous scanning probe microscopy investigations over WS_(2)and Au{111}

Individual atomic defects in 2D materials impact their macroscopic functionality.Correlating the interplay is challenging,however,intelligent hyperspectral scanning tunneling spectroscopy(STS)mapping provides a feasible solution to this technically difficult and time consuming problem.Here,dense spectroscopic volume is collected autonomously via Gaussian process regression,where convolutional neural networks are used in tandem for spectral identification.Acquired data enable defect segmentation,and a workflow is provided for machine-driven decision making during experimentation with capability for user customization.We provide a means towards autonomous experimentation for the benefit of both enhanced reproducibility and user-accessibility.Hyperspectral investigations on WS_(2)sulfur vacancy sites are explored,which is combined with local density of states confirmation on the Au{111}herringbone reconstruction.Chalcogen vacancies,pristine WS_(2),Au face-centered cubic,and Au hexagonal close-packed regions are examined and detected by machine learning methods to demonstrate the potential of artificial intelligence for hyperspectral STS mapping.

Coordination corrected ab initio formation enthalpies

The correct calculation of formation enthalpy is one of the enablers of ab-initio computational materials design.For several classes of systems(e.g.oxides)standard density functional theory produces incorrect values.Here we propose the“coordination corrected enthalpies”method(CCE),based on the number of nearest neighbor cation–anion bonds,and also capable of correcting relative stability of polymorphs.CCE uses calculations employing the Perdew,Burke and Ernzerhof(PBE),local density approximation(LDA)and strongly constrained and appropriately normed(SCAN)exchange correlation functionals,in conjunction with a quasiharmonic Debye model to treat zero-point vibrational and thermal effects.The benchmark,performed on binary and ternary oxides(halides),shows very accurate room temperature results for all functionals,with the smallest mean absolute error of 27(24)meV/atom obtained with SCAN.The zero-point vibrational and thermal contributions to the formation enthalpies are small and with different signs—largely canceling each other.