quantum mechanical approach
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Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 649
Author(s):  
Dmitrii Pankin ◽  
Mikhail Smirnov ◽  
Anastasia Povolotckaia ◽  
Alexey Povolotskiy ◽  
Evgenii Borisov ◽  
...  

This paper discusses the applicability of optical and vibrational spectroscopies for the identification and characterization of the T-2 mycotoxin. Vibrational states and electronic structure of the T-2 toxin molecules are simulated using a density-functional quantum-mechanical approach. A numerical experiment aimed at comparing the predicted structural, vibrational and electronic properties of the T-2 toxin with analogous characteristics of the structurally similar 3-deacetylcalonectrin is performed, and the characteristic spectral features that can be used as fingerprints of the T-2 toxin are determined. It is shown that theoretical studies of the structure and spectroscopic features of trichothecene molecules facilitate the development of methods for the detection and characterization of the metabolites.


Author(s):  
В.С. Михайлов ◽  
П.Ю. Бабенко ◽  
А.П. Шергин ◽  
А.Н. Зиновьев

The Auger transition probabilities are calculated while filling a vacancy on 2pπ orbital in a Ne+-Ne quasimolecule, a short-lived system which is formed when ion and atom approach each other and decays when they scatter. For the first time calculations were performed for various degrees of particles ionization in quasimolecule. It was found that with increase of collision energy and decrease of distance of the closest approach of particles the system ionization degree increases very significantly (from 2 to 6). Using of the quantum mechanical approach and taking into account the dynamics of collisions made it possible for the first time to describe quantitatively the experimental spectra of Auge electrons for a complex many-electron quasimolecule. From the whole variety of possible Auger decay channels the dominant contribution of the transition was established, from the initial 3dπ-3dπ state to the 2pπ orbital.


2021 ◽  
pp. 143-148
Author(s):  
A. Makarova ◽  
A. Buyadzhi ◽  
O. Dubrovsky

There are presented the results of  calculating the energies of the helium atom energy in a homogeneous magnetic field on the basis of the new numerical quantum-mechanical approach.  The approach is based on the numerical difference solution of the Schrödinger equation, the model potential method and the operator perturbation theory formalism. The obtained results on energy of the helium atom in dependence upon the magnetic field strength  are  compared with available  theoretical results, obtained on the basis of alternative numerical Hartree-Fock and diagonalization methods.


2021 ◽  
Vol 19 (1) ◽  
pp. 016001
Author(s):  
K B Oganesyan ◽  
M Hnatic ◽  
P Kopchancky

Abstract The theory of free electron lasers (FELs) is well developed both in quantum mechanical and classical approaches. In strophotron FEL, in classical approach, resonance frequency and the gain are strongly dependent on initial parameters of electron beam. In the quantum mechanical approach considered by Zaretsky and Nersesov (1983 JETP 57 518), there is no such dependence. The correspondence between the quantum mechanical and classical approaches in a relativistic strophotron FEL is discussed. We study the initial distribution of electrons over vibrational levels determined by the expansion coefficients in relativistic strophotron FEL. It is shown, (presenting electron wave function in the form of Gaussian wave packet), that the number of the vibrational level most efficiently populated at the initial moment of time can be expressed in terms of the initial parameters of the electron beam.


2021 ◽  
Vol 19 (50) ◽  
pp. 70-76
Author(s):  
Mohsin Al-Khaykanee ◽  
Ali Al-Jawdahb

The present work shows a theoretical results that have been used the functional Hybrid of three parameters Lee-Yang-Parr (B3LYP) of the quantum mechanical approach for density functional theory with (Spanish Initiative for Electronic Simulations with Thousands of Atoms) SIESTA code. All calculations were carried out employing the used method at the Gaussian 09 package of programs. It was reported the main point for research on dominance of the bandgap of elongated pi-conjugated molecules by using different chemical groups replacing hydrogen atom in the most molecules that used in this work. The side groups creates another factor that controls the value of the band gap. The dihedral angle between the two phenyl rings plays more important role in controlling the band gap in these molecules.


2021 ◽  
Vol 33 (2) ◽  
pp. 209-220
Author(s):  
Etienne Balan ◽  
Emmanuel Fritsch ◽  
Farid Juillot ◽  
Thierry Allard ◽  
Sabine Petit

Abstract. Although OH overtone bands of 1:1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1:1 phyllosilicates. In this case, the overtone spectra cannot be directly related to their fundamental counterparts observed in the mid-infrared (MIR) spectra. In the present study, we use a parameterized quantum-mechanical approach to compute the vibrational frequencies related to the fundamental and overtone bands in serpentine group and kaolinite group minerals. The simple model is based on a description of the vibrational properties of a cluster of OH groups in terms of harmonically coupled anharmonic oscillators. The comparison of the theoretical results with experimental observations makes it possible to interpret most of the salient features of the overtone spectrum of 1:1 phyllosilicates. Unlike the bands observed in the MIR spectra, the overtone bands observed between 7000 and 7300 cm−1 are related to local transitions from the ground state to the second excitation level of OH groups, whereas the weaker bands observed between 7300 and 7400 cm−1 involve a double excitation to the first vibrational level of OH oscillators. The results also support the assignment of specific overtone bands to the occurrence of substituted divalent cations of transition elements in serpentine group minerals.


2021 ◽  
Vol 22 (6) ◽  
pp. 3232
Author(s):  
Brigitta Elsässer ◽  
Peter Goettig

Experimental evidence for enzymatic mechanisms is often scarce, and in many cases inadvertently biased by the employed methods. Thus, apparently contradictory model mechanisms can result in decade long discussions about the correct interpretation of data and the true theory behind it. However, often such opposing views turn out to be special cases of a more comprehensive and superior concept. Molecular dynamics (MD) and the more advanced molecular mechanical and quantum mechanical approach (QM/MM) provide a relatively consistent framework to treat enzymatic mechanisms, in particular, the activity of proteolytic enzymes. In line with this, computational chemistry based on experimental structures came up with studies on all major protease classes in recent years; examples of aspartic, metallo-, cysteine, serine, and threonine protease mechanisms are well founded on corresponding standards. In addition, experimental evidence from enzyme kinetics, structural research, and various other methods supports the described calculated mechanisms. One step beyond is the application of this information to the design of new and powerful inhibitors of disease-related enzymes, such as the HIV protease. In this overview, a few examples demonstrate the high potential of the QM/MM approach for sophisticated pharmaceutical compound design and supporting functions in the analysis of biomolecular structures.


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