Revisiting the tellurium clusters (Ten; n = 2–8) using ab initio methods

2020 ◽  
Vol 98 (1) ◽  
pp. 57-64 ◽  
Author(s):  
Hassan H. Abdallah
Keyword(s):  
Ab Initio ◽  
Experimental Studies ◽  
Bond Distance ◽  
Vibrational Frequencies ◽  
Orbital Theory ◽  
B3lyp Method ◽  
Charged Clusters ◽  
Cluster Geometry ◽  
The Stability ◽  
Positively Charged

The optimized geometries and vibrational frequencies of Te clusters n = 2–8 are calculated using ab initio molecular orbital theory at B3LYP, MP2, BLYP, and BH–HLYP levels of approximation. We found that Te8 (D4d) cluster has the highest stability followed by Te7 and Te6 (D3d). The computed vibrational frequencies have small systematic deviations with IR spectra for crystalline Te5, Te6 (C2v). The stability of positively and negatively charged Te clusters is determined by the B3LYP method. This is because the B3LYP method demonstrated the best stability in every cluster geometry. In general, the results showed that the negatively charged clusters have the highest stability, followed by neutral clusters, and finally positively charged clusters. However, the predicted bond angle and bond distance for every cluster geometry displayed very close values with different levels of calculations. These calculations will provide predictions for future experimental studies.

Isolated versus Condensed Anion Structure VII: X-ray Structure Analysis of 1,3-Propanediammonium Dibromodichlorocadmate(II), [H3N(CH2)3NH3]CdBr2Cl2, and Estimation of Stability of Five-coordinated Halide Anions, MX53-(M = Cd, Zn; X = Cl, Br) by Means of Ab-initio MO Calculations

2001 ◽  
Vol 56 (9-10) ◽  
pp. 641-646 ◽  
Author(s):  
Hideta Ishihara ◽  
Toshiya Okajima ◽  
Keizo Horiuchi ◽  
Ingrid Svoboda ◽  
Hartmut Fuess
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Structure Analysis ◽  
Metal Cation ◽  
The Other ◽  
Mo Calculations ◽  
X Ray ◽  
Ab Initio Mo Calculations ◽  
The Stability ◽  
Positively Charged

Abstract The coordination capability of Cl and Br in halogenocadmate(II) complexes is estimated by a solution of the structure of 1,3-propanediammonium dibromodichlorocadmate(II). The compound crystallizes as a layered anion structure with Cl bridges and Br terminals at 293 K: Imma, a = 741.56(7), b = 1869.5(5), and c -771.55(8) pm, Z = 4. In order to explain the stronger tendency of halogenocadmate(II) complexes to form layered structures as compared to halogenozincate(II), ab-initio calculations were performed. The stability of MX53-(M = Cd, Zn; X = Cl, Br) is compared. Isolated ZnX53- and CdBr53- ions are not stable. On the other hand a trigonal bipyramid CdCl53- ion is considered to be subtly stable in the crystal mainly due to Coulomb attractive interactions between the positively charged metal cation Cd2+ in a CdCl3- fragment and two Cl- ions.

A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

2003 ◽  
Vol 68 (12) ◽  
pp. 2322-2334 ◽  
Author(s):  
Robert Vianello ◽  
Zvonimir B. Maksić
Keyword(s):  
Ab Initio ◽  
Spin Density ◽  
Density Functional ◽  
Radical Cations ◽  
Functional Study ◽  
Theory Approach ◽  
Functional Theory ◽  
Adiabatic Ionization Potential ◽  
Highest Occupied Molecular Orbital ◽  
Positively Charged

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.

scholarly journals Performance Evaluation of Heading-and-Winning Machines in the Conditions of Potash Mines

2021 ◽  
Vol 11 (8) ◽  
pp. 3444
Author(s):  
Sergey A. Lavrenko ◽  
Dmitriy I. Shishlyannikov
Keyword(s):  
Energy Efficiency ◽  
Experimental Studies ◽  
Efficiency Coefficient ◽  
Mechanized Method ◽  
Methodological Approaches ◽  
The Stability ◽  
Technical Solutions ◽  
Potash Mine ◽  
Complex Indicators ◽  
Potassium Magnesium

The authors focus on the process of potash ore production by a mechanized method. They show that currently there are no approved procedures for assessing the performance of heading-and-winning machines operating in the conditions of potash mines. This causes difficulties in determining the field of application of heading-and-winning machines, complicates the search for implicit technical solutions for the modernisation of existing models of mining units, prohibits real-time monitoring of the stability of stope-based technological processes and makes it difficult to assess the performance of the services concerning mining enterprises. The work represents an aggregate assessment of the performance of heading-and-winning machines for potash mines by determining complex indicators describing the technological and technical levels of organising the work in stopes. Such indicators are the coefficients of productivity and energy efficiency, respectively. Experimental studies have been carried out in the conditions of the potash mine of the Verkhnekamskoye potassium-magnesium salt deposit to assess the performance of the latest and most productive Ural-20R heading-and-winning machines manufactured in Russia. Using the above methodological approaches, this paper shows that the unsatisfactory technological performance of the studied machine is due to the low productivity of the mine district transport. The average productivity coefficient was 0.29. At the same time, high values of the energy efficiency coefficient show that the productivity of the machine is on par with design conditions.

Ab Initio Study of the Stability of the Ylide-like Intermediate Methyleneoxonium in the Reaction between Singlet Methylene and Water

1996 ◽  
Vol 118 (23) ◽  
pp. 5408-5411 ◽  
Author(s):  
Carlos Gonzalez ◽  
Albeiro Restrepo-Cossio ◽  
Manuel Márquez ◽  
Kenneth B. Wiberg
Keyword(s):  
Ab Initio ◽  
Ab Initio Study ◽  
The Stability ◽  
Singlet Methylene

scholarly journals Amine substitution into sulfuric acid – ammonia clusters

2012 ◽  
Vol 12 (8) ◽  
pp. 3591-3599 ◽  
Author(s):  
O. Kupiainen ◽  
I. K. Ortega ◽  
T. Kurtén ◽  
H. Vehkamäki
Keyword(s):  
Sulfuric Acid ◽  
Base Substitution ◽  
Free Energies ◽  
Dynamics Model ◽  
Base Exchange ◽  
Charged Cluster ◽  
Charged Clusters ◽  
Evaporation Dynamics ◽  
Ammonia Clusters ◽  
Positively Charged

Abstract. The substitution of ammonia by dimethylamine in sulfuric acid – ammonia – dimethylamine clusters was studied using a collision and evaporation dynamics model. Quantum chemical formation free energies were computed using B3LYP/CBSB7 for geometries and frequencies and RI-CC2/aug-cc-pV(T+d)Z for electronic energies. We first demonstrate the good performance of our method by a comparison with an experimental study investigating base substitution in positively charged clusters, and then continue by simulating base exchange in neutral clusters, which cannot be measured directly. Collisions of a dimethylamine molecule with an ammonia containing positively charged cluster result in the instantaneous evaporation of an ammonia molecule, while the dimethylamine molecule remains in the cluster. According to our simulations, a similar base exchange can take place in neutral clusters, although the overall process is more complicated. Neutral sulfuric acid – ammonia clusters are significantly less stable than their positively charged counterparts, resulting in a competition between cluster evaporation and base exchange.

On the stability of the cuboid singlet (S2)4 supermolecule: Benchmark ab initio studies

2013 ◽  
Vol 138 (9) ◽  
pp. 094317 ◽  
Author(s):  
A. J. Ochoa-Calle ◽  
R. Hernández-Lamoneda ◽  
A. Ramírez-Solís
Keyword(s):  
Ab Initio ◽  
The Stability

scholarly journals Extended-State-Observer-Based Super Twisting Control for Pneumatic Muscle Actuators

Actuators ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 35
Author(s):  
Yu Cao ◽  
Zhongzheng Fu ◽  
Mengshi Zhang ◽  
Jian Huang
Keyword(s):  
Control Method ◽  
Experimental Studies ◽  
State Observer ◽  
Extended State Observer ◽  
Extended State ◽  
Pneumatic Muscle ◽  
System States ◽  
The Stability ◽  
Twisting Control ◽  
Muscle Actuators

This paper presents a tracking control method for pneumatic muscle actuators (PMAs). Considering that the PMA platform only feedbacks position, and the velocity and disturbances cannot be observed directly, we use the extended-state-observer (ESO) for simultaneously estimating the system states and disturbances by using measurable variables. Integrated with the ESO, a super twisting controller (STC) is design based on estimated states to realize the high-precision tracking. According to the Lyapunov theorem, the stability of the closed-loop system is ensured. Simulation and experimental studies are conducted, and the results show the convergence of the ESO and the effectiveness of the proposed method.

Calculating Fundamental Vibrational Frequencies of Rutile by Combining Ab Initio Method with GF Matrix Method

1994 ◽  
Vol 05 (02) ◽  
pp. 299-301
Author(s):  
Lin Libin ◽  
Zheng Xiangyin
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Matrix Method ◽  
Cluster Model ◽  
Normal Modes ◽  
Vibrational Frequencies ◽  
Ab Initio Method ◽  
Environment Factor ◽  
Factor Α ◽  
Good Agreement

Based on cluster model, we have calculated the fundamental vibrational frequencies of rutile by combining ab initio method and Wilson’s GF-matrix method. In the calculation, we have introduced the concept of environment factor α to correct the force field of the cluster model. The results of calculation are in good agreement to the experimental data and the normal modes give us clear physical picture of the crystal vibration.

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