Atomic polarization phenomena impinge upon a number of areas and processes in physics. The dielectric constant and refractive index of any gas are examples of macroscopic properties that are largely determined by the dipole polarizability. When it comes to microscopic phenomena, the existence of alkaline-earth anions and the recently discovered ability of positrons to bind to many atoms are predominantly due to the polarization interaction. An imperfect knowledge of atomic polarizabilities is presently looming as the largest source of uncertainty in the new generation of optical frequency standards. Accurate polarizabilities for the group I and II atoms and ions of the periodic table have recently become available by a variety of techniques. These include refined many-body perturbation theory and coupled-cluster calculations sometimes combined with precise experimental data for selected transitions, microwave spectroscopy of Rydberg atoms and ions, refractive index measurements in microwave cavities, ab initio calculations of atomic structures using explicitly correlated wavefunctions, interferometry with atom beams and velocity changes of laser cooled atoms induced by an electric field. This review examines existing theoretical methods of determining atomic and ionic polarizabilities, and discusses their relevance to various applications with particular emphasis on cold-atom physics and the metrology of atomic frequency standards.

https://iopscience.iop.org/article/10.1088/0953-4075/43/20/202001/pdf

Theory and applications of atomic and ionic polarizabilities

A 2018 update of the most accurate calculated and experimental static dipole polarizabilities of the neutral atoms in the Periodic Table from nuclear charge Z = 1 to 120 is given. Periodic ...

https://www.tandfonline.com/doi/pdf/10.1080/00268976.2018.1535143

2018 Table of static dipole polarizabilities of the neutral elements in the periodic table

Small-core ten-valence electron energy-consistent scalar- and two-component relativistic pseudopotentials for the alkaline-earth elements from Ca to Ra are presented The accuracy and reliability of these pseudopotentials are discussed in terms of their ability to reproduce all-electron calculated and experimental dipole polarizabilities and ionization potentials

Relativistic small-core energy-consistent pseudopotentials for the alkaline-earth elements from Ca to Ra.

Increasing evidence suggests the utility of magnetic resonance imaging (MRI) as an important technique for the diagnosis of Alzheimer’s disease (AD) and for predicting the onset of this neurodegenerative disorder. In this study, we present a sophisticated machine learning (ML) model of great accuracy to diagnose the early stages of AD. A total of 373 MRI tests belonging to 150 subjects (age ≥ 60) were examined and analyzed in parallel with fourteen distinct features related to standard AD diagnosis. Four ML models, such as naive Bayes (NB), artificial neural networks (ANN), K-nearest neighbor (KNN), and support-vector machines (SVM), and the receiver operating characteristic (ROC) curve metric were used to validate the model performance. Each model evaluation was done in three independent experiments. In the first experiment, a manual feature selection was used for model training, and ANN generated the highest accuracy in terms of ROC (0.812). In the second experiment, automatic feature selection was conducted by wrapping methods, and the NB achieved the highest ROC of 0.942. The last experiment consisted of an ensemble or hybrid modeling developed to combine the four models. This approach resulted in an improved accuracy ROC of 0.991. We conclude that the involvement of ensemble modeling, coupled with selective features, can predict with better accuracy the development of AD at an early stage.

/pdf/a-comprehensive-machine-learning-model-applied-to-magnetic-1wq7rw99ku.pdf

A Comprehensive Machine-Learning Model Applied to Magnetic Resonance Imaging (MRI) to Predict Alzheimer's Disease (AD) in Older Subjects.

This chapter reviews possible experimental aspects of relativistic effects in heavier Main Group elements and their compounds. Attention is focused on the sixth, sev- enth and eighth Period elements, for which the relativistic contribution to their physical and chemical properties is significant. Superheavy elements through Z D 120 are also discussed. This review may increase interest of theoreticians in chemistry-oriented problems that require use of relativistic methods of quantum chemistry.

/pdf/relativistic-effects-and-the-chemistry-of-the-heaviest-main-1ileyzjmig.pdf

Relativistic Effects and the Chemistry of the Heaviest Main-Group Elements.

Static polarizabilities, α, and static second hyperpolarizabilities, γ, of the rare gas atoms, He–Rn, are investigated
 employing CCSD(T) calculations and large basis sets. For the lighter atoms, He–Kr, x-aug-cc-pVXZ
 basis sets were employed in order to test convergence (x = s–5; X = D–6). Further basis sets were employed for He in order
 to investigate basis set requirements. For the heavier species, effective core potentials (ECPs) are employed,
 together with a large, flexible
 valence space. α
 and γ were obtained by fitting
 the energies to standard expressions.

Static dipole polarizabilities (α) and static second hyperpolarizabilities (γ) of the rare gas atoms (He–Rn)

High-level [RCCSD(T)]
ab initio calculations are employed to generate sets of data from which spectroscopic constants for the title species could be derived. For O, the standard aug-cc-pV5Z (no h) basis set was employed, while for the metal atoms an effective core potential combined with a large, flexible valence basis set was used. Calculated ionization energies for the metal atoms, and the calculated electron affinity of O suggest that both types of basis set are performing well. The calculated constants are, in general, in good agreement with previous experimental and theoretical studies, where available. A simple ionic model is employed to obtain ionization energies, and the resulting values are compared to those calculated at the RCCSD(T) level, as well as previous experimental values. Finally, dissociation energies of the title species are also calculated.

An ab initio study of RbO, CsO and FrO (X2Σ+; A2Π) and their cations (X3Σ−; A3Π)

NO·CH4 and NO·CD4 were studied in a molecular beam, using (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy. A detailed spectrum results in each case, with a series of bands observed, assigned to intermolecular vibrations onto which is superimposed further structure. The origin of this further structure is discussed in the light of previous studies. From the spectrum, a number of intermolecular vibrational frequencies in the A state were obtained. D0′ for NO·CH4 (NO·CD4) was measured as 211 (238) cm−1; with D0″ for NO·CH4 (NO·CD4) being derived as 117 (122) cm−1. Ab initio
 calculations were performed on the state, and it is deduced that the state has a Cs global minimum, with the NO pointing towards a CH3
 face, with the N tilted towards the methane. That said, from the energetic proximity of a number of stationary points, the complex is expected to be performing wide amplitude motion, sampling a wide range of energies even with the zero-point energy.

The Ã2Σ+ ← X 2Π transition of the NO-CH4 and NO-CD4 complexes

The heaviest group 2 difluoride, radium difluoride (RaF2), is studied for the first time. A basis set is employed for radium that combines an effective core potential with a large, flexible valence space. This basis set is tested by calculating the first and second ionization energies of Ra, where values in excellent agreement with experiment are obtained. MP2 ab initio calculations are employed to obtain the optimized equilibrium geometry and the harmonic vibrational frequencies for the ground-state neutral and some of the low-lying cationic states. In addition, the optimized geometry of the ground-state neutral is obtained at the CCSD(T) level. The trend in geometry of the group 2 difluorides is confirmed, with a angle ?FRaF bond angle of 118? degrees being calculated, together with a bond length of 2.30 ?. It is concluded that involvement of the Ra 6p orbitals in the valence molecular orbitals of RaF2 adequately explains its bent geometry. RCCSD(T) calculations are then employed to calculate ionization energies. The first adiabatic ionization energy, corresponding to the ionization X~2?u+?X~1A1 is calculated to be 10.67 +/- 0.05 eV. The ordering of the ionic states is discussed in the light of the present results. The polarizability of Ra was calculated to be 36.3 ?3, with that of Ra2+ was calculated to be 1.97 ?3; the latter was employed in a simple ionic model, but this failed to calculate the ionization energy accurately.

The Heaviest Group 2 Difluoride, RaF2: Geometry and Ionization Energy

We use high-level ab initio, up to RCCSD(T), and the density functional theory (DFT) method, B3LYP, to obtain the geometry, vibrational frequencies, and heats of formation of NaO3(X~2B1) and NaO3+(X~1A1). In both cases, a C-2v, diamond structure is deduced. These values allow us also to derive the adiabatic ionization energy. We obtain the following values: ?Hf[NaO3,0K] = -13 ± 2 kcal mol-1, ?Hf[NaO3+,0K] = 167 ± 2 kcal mol-1, and AIE(NaO3) = 7.80 ± 0.05 eV. In addition, it was found that the B3LYP functional performs very well for the O-3(-) species: both geometry and vibrational frequencies. For O-3, the method performed well for the geometry, but not so well for the vibrational frequencies. Comparison is made where appropriate to experimental data and to previous calculations. Finally, ?Hr is calculated for a range of reactions that may contribute to the formation of NaO3 or NaO3+ in the atmosphere.

Structures and vibrational frequencies of NaO3 and NaO3+: the ionization energy of NaO3

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