scholarly journals Extensions of the applicability of the MMX molecular modelling system to determination of barriers to rotation of π-bonded ligands

1995 ◽  
Vol 73 (7) ◽  
pp. 1078-1083 ◽  
Author(s):  
Joel Polowin ◽  
Robert Poe ◽  
Michael C. Baird
Keyword(s):  
Molecular Mechanics ◽  
Molecular Modelling ◽  
Conformational Energy ◽  
Energy Profile ◽  
Arene Ligands ◽  
Energy Profiles ◽  
Keywords Molecular Mechanics ◽  
Modelling System ◽  
The Way

The commercially available molecular mechanics package PCMODEL, which has been shown to be very useful for determining conformational energy profiles for rotation of σ-bonded ligands, cannot be utilized to determine barriers to rotation of π-bonded ligands because of limitations in the way the π-bonding interactions are defined. This paper describes a partially successful modification of the dihedral driver of PCMODEL that makes possible reasonable calculations of the conformational energy profiles for rotation of the π-bonded arene ligands in the compounds (η6-arene)Cr(CO)2(PPh3) (arene = C6H6, C6Me6) and of the π-bonded ethylene ligands in [PtCl3(η2-CH2=CH2)]− and [(η5-C5H5)Re(NO)(PPh3)(η2-CH2=CH2)]+. The steric barriers to ethylene rotation in the latter two complexes were found to be small relative to the electronic barriers to ligand rotation. Keywords: molecular mechanics, olefin rotation, conformational energy profile.

On-the-Fly Determination of Active Region Centers in Adaptive-Partitioning QM/MM

2020 ◽  
Author(s):  
Zenghui Yang
Keyword(s):  
Quantum Mechanics ◽  
Active Region ◽  
Molecular Mechanics ◽  
Active Regions ◽  
Available Energy ◽  
Adaptive Partitioning ◽  
Different Levels

Quantum mechanics/molecular mechanics (QM/MM) methods partition the system into active and environmental regions and treat them with different levels of theory, achieving accuracy and efficiency at the same time. Adaptive-partitioning (AP) QM/MM methods allow on-the-fly changes to the QM/MM partitioning of the system. Many of the available energy-based AP-QM/MM methods partition the system according to distances to pre-chosen centers of active regions. For such AP-QM/MM methods, I develop an adaptive-center (AC) method that allows on-the-fly determination of the centers of active regions according to general geometrical or potential-related criteria, extending the range of application of energy-based AP-QM/MM methods to systems where active regions may occur or vanish during the simulation.

Free energy profile analysis to identify factors activating the aggregation-induced emission of a cyanostilbene derivative

2021 ◽  
Author(s):  
Norifumi Yamamoto
Keyword(s):  
Free Energy ◽  
Profile Analysis ◽  
Energy Profile ◽  
Contributing Factors ◽  
Free Energy Profile ◽  
Aggregation Induced Emission ◽  
Energy Profiles ◽  
Free Energy Profiles

The contributing factors that cause the aggregation-induced emission (AIE) are determined by identifying characteristic differences in the free energy profiles of the AIE processes of the AIE-active E-form of CN-MBE and the inactive Z-form.

scholarly journals Universal Synthesizer of Mueller Matrices Based on the Symmetry Properties of the Enpolarizing Ellipsoid

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 983
Author(s):  
José J. Gil ◽  
Ignacio San José
Keyword(s):  
Mathematical Structure ◽  
Mueller Matrix ◽  
Morphological Properties ◽  
Nondestructive Analysis ◽  
Structural Decomposition ◽  
Symmetry Properties ◽  
Mueller Matrices ◽  
Scattering Measurement ◽  
The Way

Polarimetry is today a widely used and powerful tool for nondestructive analysis of the structural and morphological properties of a great variety of material samples, including aerosols and hydrosols, among many others. For each given scattering measurement configuration, absolute Mueller polarimeters provide the most complete polarimetric information, intricately encoded in the 16 parameters of the corresponding Mueller matrix. Thus, the determination of the mathematical structure of the polarimetric information contained in a Mueller matrix constitutes a topic of great interest. In this work, besides a structural decomposition that makes explicit the role played by the diattenuation-polarizance of a general depolarizing medium, a universal synthesizer of Muller matrices is developed. This is based on the concept of an enpolarizing ellipsoid, whose symmetry features are directly linked to the way in which the polarimetric information is organized.

scholarly journals III. Further experiments on the vapour densities of potassium and sodium

1879 ◽  
Vol 29 (196-199) ◽  
pp. 490-493 ◽  
Keyword(s):  
Considerable Error ◽  
Exact Determination ◽  
The Way

In one former communication “On the Vapour Densities of Potas­sium and Sodium,” we pointed out the chief obstacles which lay in the way of an exact determination of these constants. Having overcome the chief manipulative difficulties in connexion with the method we described, there still remained the problem for solution as to how far the use of iron bottles in our experiments might affect the results. If the iron retained the metals or allowed their vapours to diffuse with rapidity through it, a considerable error might be produced without its being easily detected.

On the Inadequacy of existing Data for determining the Rate of Mortality among Select Lives

1854 ◽  
Vol 4 (1) ◽  
pp. 1-9
Author(s):  
William Spens
Keyword(s):  
First Year ◽  
Sufficient Data ◽  
Existing Data ◽  
Selection Of ◽  
The Way

I. While so much improvement has recently taken place in the arrangement and construction of various tables for facilitating calculations founded on existing data, very little has been done in the way of investigating and correcting the data themselves; and it is feared that the question of the rate of mortality among select lives is still involved in the greatest doubt and obscurity.II. It is not proposed in the present paper to go farther than to show that the rate of mortality, during the first year of selection, of select assured lives is so materially different from what it has hitherto been represented, as to lead to the inference that the data from which the erroneous deduction has been made cannot be true data for the ascertainment of the value of selection. To investigate the rate of mortality of select lives at separate ages, I conceive to be of the utmost importance for the elucidation of truth, and the proper direction of sanatory inquiries; but I do not consider that sufficient data at present exist for the determination of this, and these can only be obtained by a united inquiry. I shall be very happy if the present observations have any effect in hastening such an investigation, which sooner or later must be entered upon.

Study on Calculation of Rock Pressure and Determination of Depth for Shallow Asymmetric Tunnel

2011 ◽  
Vol 261-263 ◽  
pp. 1034-1038 ◽  
Author(s):  
Xiao Jun Zhou
Keyword(s):  
Rock Pressure ◽  
Calculation Method ◽  
Tunnel Structure ◽  
The Way

The method to calculate rock pressure for shallow asymmetric tunnel is analyzed by means of taking a mountainous tunnel with semicircular crown and straight sidewall as the object in this paper. The calculation method of tunnel rock pressure has been presented with consideration of both tunnel structure size and its overburden depth. Finally the way to determine the shallow or profound depth of asymmetric tunnel is also obtained.

scholarly journals Statistical error in counting experiments

1935 ◽  
Vol 149 (868) ◽  
pp. 467-486 ◽  
Keyword(s):  
Finite Number ◽  
Statistical Error ◽  
Single Particles ◽  
Exact Determination ◽  
Statistical Laws ◽  
The Way

Experiments in which single particles are studied with the aid of counters would, in principle, lead to an exact determination of the statistical laws governing the behaviour of these particles if the number of counted particles were infinitely large. With a finite number of counts, however, a finite statistical error will always remain. This error depends upon the number of counts and upon the way in which one makes use of the counter readings to calculate the parameters entering into the statistical laws. The purpose of the following investigation is to show for some typical cases which way of calculating has to be adopted in order to make the error a minimum.

scholarly journals Direct Determination of Ascorbic Acid in a Grapefruit: Paving the Way for In Vivo Spectroelectrochemistry

2017 ◽  
Vol 89 (3) ◽  
pp. 1815-1822 ◽  
Author(s):  
Jesus Garoz-Ruiz ◽  
Aranzazu Heras ◽  
Alvaro Colina
Keyword(s):  
Ascorbic Acid ◽  
Direct Determination ◽  
The Way
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