The structure of the diatomic molecular solids

1974 ◽  
Vol 340 (1620) ◽  
pp. 57-80 ◽  
Keyword(s):  
Thermal Effects ◽  
Molecular Shape ◽  
Stable Structure ◽  
Crystallographic Structure ◽  
Molecular Solids ◽  
Quadrupole Moments ◽  
Lennard Jones ◽  
Parameter Values ◽  
Atom Potential ◽  
Great Simplicity

A simple model of the low temperature phases of the diatomic molecular solids is examined. The model consists of molecules, interacting via a Lennard-Jones atom-atom potential and quadrupole-quadrupole interactions. The internal energy of any crystallographic structure (excluding thermal effects) can then be given in terms of two dimensionless parameters, which describe the deviation of the molecular shape from a sphere and the relative importance of the quadrupole energy. The minimum energies and optimum molecular configurations in several structures are computed, for values of these dimensionless variables which span the values appropriate to the actual homonuclear diatomic molecular solids, H 2 , N 2 , O 2 , F 2 , Cl 2 , Br 2 and I 2 . Despite its great simplicity, the model is able to explain several features of these structures. These are (i) o -H 2 and N 2 have the optimum quadrupole structure, Pa3; (ii) β-O 2 is one of the optimum van der Waals’ structures, R3 ¯ m; (iii) the monoclinic α-F 2 structure is the most stable structure for parameter values very close to those appropriate to F 2 ; (iv) the ortho-rhombic Cmca structure (observed for Cl 2 , Br 2 and I 2 ) is the most stable structure for a large range of quadrupole moments which may be appropriate to these molecules. The model, is, of course, unable to take into account intermolecular bonding or spin-dependent interatomic forces. The former is important for the halogens and the latter for the (magnetic) oxygen molecule. The case of α-O 2 is treated in the following paper.

Intermolecular potentials from NMR data: H2–N2O and H2–CO2

1983 ◽  
Vol 61 (5) ◽  
pp. 664-670 ◽  
Author(s):  
Lakshman Pandey ◽  
C. P. K. Reddy ◽  
K. Lalita Sarkar
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Intermolecular Potential ◽  
Quadrupole Moments ◽  
Spin Lattice ◽  
Lennard Jones ◽  
Nmr Data ◽  
Potential Parameters

Proton spin-lattice relaxation times T1 were measured in mixtures of H2 with N2O as a function of density, composition, and temperature (200–400 K) in the region where [Formula: see text]. These data, along with the data obtained by Lalita and Bloom for H2–CO2, were interpreted, using Bloom–Oppenheim theory, to obtain the anisotropic intermoleeular potential parameters. Two models, (i) the Lennard–Jones (12–6) potential (LJP) and (ii) the modified Buckingham (exp-6) potential (MBP), were used to represent the isotropic part of the intermolecular potential. The relative anisotropy in the attractive r−6 term and the quadrupole moments of N2O and CO2 as obtained from MBP model are in better agreement with the values obtained from the polarizability data and the reported values, respectively, than those obtained from the LJP model.

ROLE OF INTERACTION ON NOISE-INDUCED TRANSPORT OF TWO COUPLED PARTICLES IN BROWNIAN RATCHET DEVICES

2006 ◽  
Vol 06 (03) ◽  
pp. L263-L277 ◽  
Author(s):  
RENATA RETKUTE ◽  
JAMES P. GLEESON
Keyword(s):  
Classical Case ◽  
Transport Processes ◽  
Common Assumption ◽  
Lennard Jones ◽  
Brownian Particles ◽  
Flashing Ratchet ◽  
Analytical Formulas ◽  
Type Interaction ◽  
Parameter Values

The motion of elastically coupled Brownian particles in ratchet-like potentials has attracted much recent interest due to its application to transport processes in many fields, including models of DNA polymers. We consider the influence of the type of interacting force on the transport of two particles in a one-dimensional flashing ratchet. Our aim is to examine whether the common assumption of elastic coupling captures the important features of ratchet transport when the inter-particle forces are more complex. We compare Lennard-Jones type interaction to the classical case of elastically coupled particles. Numerical simulations agree with analytical formulas for the limiting cases where the coupling is very weak or very strong. Parameter values where the Lennard-Jones force is not well approximated by a linearization of the force about the equilibrium distance are identified.

scholarly journals Superconducting Properties of Bi2-xPb0.3WxSr2Ca2Cu3O10+ Compounds

2021 ◽  
pp. 490-495
Author(s):  
Mohammed J. Tuama ◽  
Lamia K. Abbas
Keyword(s):  
Volume Fraction ◽  
Solid State Reaction Method ◽  
Lattice Parameter ◽  
Crystallographic Structure ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
X Ray ◽  
Two Phases ◽  
Parameter Values

The conventional solid-state reaction method was utilized to prepare a series of superconducting samples of the nominal composition Bi2-xPb0.3WxSr2Ca2Cu3O10+d with 0≤x≤0.5 of 50 nm particle size of tungsten sintered at 8500C for 140h in air . The influence of substitution with W NPs at bismuth (Bi) sites was characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and dc electrical resistivity. Room temperature X-ray diffraction analysis revealed that there exists two phases, i.e. Bi-(2223) and Bi-(2212), in addition to the impurity phases of (SrCa) 2Cu2O3, Sr2Ca2Cu7Oδ, Ca2PbO4, CaO, and WO. It was found that the crystallographic structure of all samples was orthorhombic. Lattice parameter values and the volume fraction of the (2223)-phase of the prepared samples were also calculated. The superconductivity transition temperature (Tc) for samples subjected to substitution with W NPs was found to be higher than that for the pure sample. The optimal value of W NPs content in (Bi, Pb)-2223 system was found to be at x=0.3. 

Monte-Carlo Simulation of Nitrogen

1976 ◽  
Vol 31 (9) ◽  
pp. 1108-1112 ◽  
Author(s):  
S. Romano
Keyword(s):  
Computer Simulation ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Monte Carlo Method ◽  
Liquid Nitrogen ◽  
Molecular Vibration ◽  
Lennard Jones ◽  
The Subject ◽  
Atom Potential

Abstract The subject of the present paper is computer simulation of a-solid and liquid nitrogen, using a Lennard-Jones atom-atom potential and the isothermal-isobaric Monte-Carlo method. Two sets of calculations were performed, both at the same pressure (1 atm) and temperatures (a-solid at 25 and 35.6 K, liquid at 63.15 and 77.35 K). In the first set the molecules are assumed to be rigid, whereas in the second they are allowed to vibrate; the molecular vibration is treated classically and as-sumed to be harmonic. Comparison are mode between the two models and with experiment.

scholarly journals Cutting Speed and Feed Influence on Surface Microhardness of Dry-Turned UNS A97075-T6 Alloy

2020 ◽  
Vol 10 (3) ◽  
pp. 1049 ◽  
Author(s):  
Sergio Martín-Béjar ◽  
Francisco Javier Trujillo Vilches ◽  
Carolina Bermudo Gamboa ◽  
Lorenzo Sevilla Hurtado
Keyword(s):  
Surface Roughness ◽  
Thermal Effects ◽  
General Trend ◽  
Cutting Speed ◽  
Cutting Parameters ◽  
Corrosion Process ◽  
Surface Microhardness ◽  
Before And After ◽  
Dry Conditions ◽  
Parameter Values

In this work, an analysis of the cutting speed and feed influence on surface roughness and microhardness of UNS A97075-T6 alloy, turned under dry conditions, was carried out. The results were compared before and after a corrosion process. The influence of these cutting parameters on each of these variables was analyzed, as well as the possible interrelation between them. The microgeometrical deviations showed a general trend to increase with feed. However, no significant modifications were observed as a function of the cutting speed. This trend was softer after the corrosion process, due to the surface alterations produced by pitting corrosion, which resulted in higher dispersion of the experimental data. In addition, a surface microhardness increment was observed in all samples, after machining and before corrosion, regardless of the cutting parameter values. The experimental results revealed that the mechanical effects, produced by the feed, should not be neglected against the thermal effects, produced by the cutting speed, within the range of the tested cutting speed. Finally, the corrosion process negatively affected the microhardness, but it was not possible to establish a direct relationship between the cutting parameters, surface roughness, and microhardness after a corrosion process.

A critical evaluation of Lennard–Jones and Stockmayer potential parameters and of some correlation methods

1977 ◽  
Vol 55 (16) ◽  
pp. 3007-3020 ◽  
Author(s):  
Frank M. Mourits ◽  
Frans H. A. Rummens
Keyword(s):  
Critical Evaluation ◽  
Viscosity Data ◽  
Priority Rules ◽  
Viscosity Measurements ◽  
Lennard Jones ◽  
Correlation Methods ◽  
Correlation Techniques ◽  
Parameter Values ◽  
Potential Parameters

Published values for the potential parameters σ and ε/k of the Lennard–Jones (12–6) and Stockmayer (12–6–3) potentials as based on viscosity measurements are reviewed, with particular reference to the problem of indeterminacy inherent to such calculations. A number of correlation techniques, calibrated on viscosity-based potential parameters, are critically reviewed; where possible, priority rules for the use of these correlations have been developed. In addition, several other criteria (i.e. not based on viscosity data) for the acceptance or rejection of σ and ε/k parameter values are also discussed. Upon application of the various criteria and priority rules it has been possible to give recommended σ and ε/k parameter values for 75 molecules.

A Lennard-Jones embedded-atom potential and its application to the study of melting

2002 ◽  
Vol 11 (2) ◽  
pp. 139-143 ◽  
Author(s):  
Wang Tun ◽  
Zhou Fu-Xin ◽  
Liu Yue-Wu
Keyword(s):  
Lennard Jones ◽  
Embedded Atom ◽  
Atom Potential

Computer simulations of polyatomic molecules II. Molecular dynamics studies of diatomic liquids with atom-atom and quadrupole-qiiadrupole potentials

1977 ◽  
Vol 355 (1681) ◽  
pp. 239-266 ◽  
Keyword(s):  
Molecular Dynamics ◽  
Pair Correlation ◽  
Quadrupole Moments ◽  
Lennard Jones ◽  
Dependent Pair ◽  
Liquid Bromine ◽  
Homonuclear Diatomic Molecules ◽  
Quadrupole Term ◽  
Repulsive Forces ◽  
Orientational Structure

The molecular dynamics method has been used to study a model system of 256 homonuclear diatomic molecules governed by intermolecular potentials of the form U = UAA + Z7QQ, where UAA is an atom-atom potential and C/QQ is the quadrupole-quadrupole potential. For UAA both the full Lennard-Jones and the repulsive part only of the Lennard-Jones potential have been used, and C7QQ has been used with reduced quadrupole moments, Q* = $/(e L* = L/cr (bond length/atom diameter) between 0.33 and 0.63 have been studied, at reduced temperatures * =kT/e from 0.98 to 3.48 and reduced densities p* = pal from 0.522 to 1.043 (where ae is the diameter of a sphere having a volume equal to that of the diatomic). Detailed orientational structure in the liquid has been examined by calculating as many as 22 terms in the spherical harmonic expansion of the angle dependent pair distribution function. At short distances these systems exhibit a high degree of angular correlation, which increases with increasing elongation and density. Pair correlation functions calculated from the Lennard-Jones and Lennard-Jones repulsive models are virtually identical, other parameters being equal, and are similar to those for hard diatomics, indicating that both radial and orientational structure are determined mainly by short-range repulsive forces. The addition of a moderately strong quadrupole term to the potential produces dramatic changes in structure and significant changes in thermodynamic properties. A potential with a moderately strong quadrupole term is found to give the correct qualitative features for the structure factor of liquid bromine.

Potential energy calculations of the rotational barriers of molecular solids. II. The dynamic structures of adamantane and hexamethylenetetramine in the solid state and the nature of the phase transition in adamantane

1976 ◽  
Vol 54 (5) ◽  
pp. 769-782 ◽  
Author(s):  
C. A. Fyfe ◽  
D. Harold-Smith
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Crystal Structure Data ◽  
Molecular Solids ◽  
Detailed Consideration ◽  
Disordered Structure ◽  
Potential Energy Calculations ◽  
Dynamic Structures ◽  
Experimental Values ◽  
Atom Potential

Nonbonded atom–atom potential functions have been used in conjunction with literature crystal structure data from diffraction measurements to calculate the sublimation energies and also the energy barriers for rotation around the molecular axes for both α and β phases of adamantane and also for hexamethylenetetramine. These results are compared with experimental values and the nature of the dynamic structures deduced.In addition, a detailed consideration of individual intermolecular interactions in the case of adamantane is presented which explains in detail the observed high temperature disordered structure and the nature of the associated order–disorder transition.

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