Force Fields with Fixed Bond Lengths and with Flexible Bond Lengths: Comparing Static and Dynamic Fluid Properties

2020 ◽  
Vol 65 (4) ◽  
pp. 1583-1593 ◽  
Author(s):  
Matthias Fischer ◽  
Gernot Bauer ◽  
Joachim Gross
Keyword(s):  
Force Fields ◽  
Bond Lengths ◽  
Fluid Properties ◽  
Fixed Bond

The Future

1992 ◽  
Author(s):  
John A. Tossell ◽  
David J. Vaughan
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Force Fields ◽  
Structural Characteristics ◽  
Future Research ◽  
Quantum Mechanical ◽  
Bond Lengths ◽  
Hartree Fock ◽  
Qualitative Level ◽  
Dynamics Simulations

In this final chapter, an attempt is made to provide an overview of the capabilities of quantum-mechanical methods at the present time, and to highlight the needs for future development and possible future applications of these methods, particularly in areas related to mineral structures, energetics, and spectroscopy. There is also a brief account of some new areas of application, specific directions for future research, and possible developments in the perception and use of quantum-mechanical approaches. The book ends with an epilog on the overall role of “theoretical geochemistry” in the earth and environmental sciences. The local structural characteristics of minerals such as Mg2SiO4, which contain only main-group elements, are reasonably well reproduced by ab initio Hartree-Fock-Roothaan (SCF) cluster calculations at the mediumbasis- set level. Calculations incorporating configuration interaction will inevitably follow and probably lead to somewhat better agreement with experiment. The most pressing needs in this area of study are for the development of systematic procedures for cluster selection and embedding, for a greater understanding of the results at a qualitative level, and for more widespread efficient application of the quantum-chemical results currently available. In the last area, substantial progress has already been made by Lasaga and Gibbs (1987), Sanders et al. (1984), Tsuneyuki et al. (1988), and others, who have used ab initio calculations to generate theoretical force fields which can then be used in molecular-dynamics simulations. If the characteristics of the resultant force fields can be understood at a first-principles level, then it may be possible to understand details of the simulated structures at the same level. Unfortunately, as regards a greater qualitative understanding of the quantum-mechanical calculations, little progress has been made. Rather old qualitative theories describe some aspects of bond-angle variation (Tossell, 1986), but no general model to interpret variations in bond lengths has been developed within either chemistry or geochemistry beyond the model of additive atomic (Slater) or ionic (Shannon and Prewitt) radii. Indeed, global theories of bond-length variations within an ab initio framework seem to be nonexistent. Nonetheless, quantum-chemical studies have shown the presence of intriguing systematics in bond lengths (Gibbs et al., 1987), which had been already noted empirically.

Protium -Deuterium Fractionation Factors for Organic Molecules Calculated From Vibrational Force Fields

1989 ◽  
Vol 44 (5) ◽  
pp. 337-354
Author(s):  
Vernon J. ◽  
Shiner Jr. ◽  
Thomas E. Neumann
Keyword(s):  
Organic Molecules ◽  
Force Fields ◽  
Small Organic Molecules ◽  
Valence Force ◽  
Bond Lengths ◽  
Mechanistic Analysis ◽  
Fractionation Factors

New valence force fields have been calculated for forty-seven small organic molecules and used to calculate protium-deuterium fractionation factors. Factors for molecules of the type CH3X and HCOX have been found to correlate with the electronegativities of X and the CX bond lengths. The effects of cumulative substitution on a given C atom on the alpha CH fractionation factors have been examined. Some uses of the factors in mechanistic analysis are discussed.

Comparison of STO-3G and 3-21G ab initio harmonic force fields for ethane, propane, dimethyl ether, and cyclobutane: effects of geometry and scaling on calculated frequencies, eigenvectors, and infrared absorption intensities

1988 ◽  
Vol 66 (5) ◽  
pp. 1318-1332 ◽  
Author(s):  
R. Anthony Shaw ◽  
Charles Ursenbach ◽  
Arvi Rauk ◽  
Hal Wieser
Keyword(s):  
Force Field ◽  
Ab Initio ◽  
Dimethyl Ether ◽  
Infrared Absorption ◽  
Force Fields ◽  
Vibrational Frequencies ◽  
Harmonic Force ◽  
Scaling Factors ◽  
Bond Lengths ◽  
Optimized Geometries

Ab initio harmonic force fields were calculated for ethane, propane, dimethyl ether, and cyclobutane at the STO-3G and 3-21G levels. The calculated frequencies, displacement eigenvectors, and calculated infrared absorption intensities were compared as they derive from force constants that were (i) unsealed; (ii) scaled to fit observed vibrational frequencies reported in the literature; (iii) evaluated at the optimized geometries; and (iv) evaluated at structures for which the bond lengths were corrected from the optimized geometries according to published procedures. A total of nine combinations of ab initio force field/reference geometry/G-matrix geometry were investigated for each of the four molecules. The ability of scaling factors as the only variables to predict vibrational parameters from STO-3G and 3-21G force fields was explored. Conditions were examined for which the scaling factors are satisfactorily transferable among different molecules.

Use of the Magnetostatic Analogue In Electromagnetic Lens Engineering

1970 ◽  
Vol 28 ◽  
pp. 360-361
Author(s):  
John W. Coleman
Keyword(s):  
Boundary Conditions ◽  
High Performance ◽  
Force Fields ◽  
Optical Design ◽  
Direct Conversion ◽  
Design Engineering ◽  
Design Data ◽  
Scalar Potentials ◽  
Geometric Elements ◽  
At Will

In the design engineering of high performance electromagnetic lenses, the direct conversion of electron optical design data into drawings for reliable hardware is oftentimes difficult, especially in terms of how to mount parts to each other, how to tolerance dimensions, and how to specify finishes. An answer to this is in the use of magnetostatic analytics, corresponding to boundary conditions for the optical design. With such models, the magnetostatic force on a test pole along the axis may be examined, and in this way one may obtain priority listings for holding dimensions, relieving stresses, etc..The development of magnetostatic models most easily proceeds from the derivation of scalar potentials of separate geometric elements. These potentials can then be conbined at will because of the superposition characteristic of conservative force fields.

Innovative electrotechnological systems to provide the temperature modes of technological pipelines

2019 ◽  
Vol 2 (1) ◽  
pp. 29-39 ◽  
Author(s):  
S. G. Konesev ◽  
P. A. Khlyupin
Keyword(s):  
Induction Heating ◽  
Thermal Exposure ◽  
Heating System ◽  
The Arctic ◽  
Process Conditions ◽  
Heating Systems ◽  
Fluid Properties ◽  
Low Efficiency ◽  
Extreme North ◽  
Induction Heating System

Introduction: the systems of thermal effects on thermo-dependent, viscous and highly viscous liquids under conditions of the Arctic and the Extreme North are considered. Low efficiency and danger of heating systems based on burned hydrocarbons, heated liquids and steam are shown. Electrothermal heating systems used to maintain thermo-dependent fluids in a fluid state are considered. The evaluation of the effectiveness of the application of the most common electrothermal system — heating cables (tapes). The most effective electrothermal system based on induction technologies has been determined. Materials and methods: considered methods of thermal exposure to maintain the fluid properties of thermo-dependent fluids at low extreme temperatures. Results: presents an induction heating system and options for its implementation in the Extreme North and the Arctic. Conclusions: induction heating system to minimize loss of product quality, improve the system performance under changing process conditions, eliminate fire product, to reduce the influence of the human factor.

Reflecting the Sky in Water

2017 ◽  
Vol 3 (1) ◽  
pp. 112-126 ◽  
Author(s):  
Ilaria Cristofaro
Keyword(s):  
The Unconscious ◽  
Related Case ◽  
Quality Of Water ◽  
Fluid Properties ◽  
Phenomenological Perspective ◽  
Auto Ethnography ◽  
The Individual ◽  
Artificial Water ◽  
Land Water

From a phenomenological perspective, the reflective quality of water has a visually dramatic impact, especially when combined with the light of celestial phenomena. However, the possible presence of water as a means for reflecting the sky is often undervalued when interpreting archaeoastronomical sites. From artificial water spaces, such as ditches, huacas and wells to natural ones such as rivers, lakes and puddles, water spaces add a layer of interacting reflections to landscapes. In the cosmological understanding of skyscapes and waterscapes, a cross-cultural metaphorical association between water spaces and the underworld is often revealed. In this research, water-skyscapes are explored through the practice of auto-ethnography and reflexive phenomenology. The mirroring of the sky in water opens up themes such as the continuity, delimitation and manipulation of sky phenomena on land: water spaces act as a continuation of the sky on earth; depending on water spaces’ spatial extension, selected celestial phenomena can be periodically reflected within architectures, so as to make the heavenly dimension easily accessible and a possible object of manipulation. Water-skyscapes appear as specular worlds, where water spaces are assumed to be doorways to the inner reality of the unconscious. The fluid properties of water have the visual effect of dissipating borders, of merging shapes, and, therefore, of dissolving identities; in the inner landscape, this process may represent symbolic death experiences and rituals of initiation, where the annihilation of the individual allows the creative process of a new life cycle. These contextually generalisable results aim to inspire new perspectives on sky-and-water related case studies and give value to the practice of reflexive phenomenology as crucial method of research.

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