Ab Initio Calculations of New α-L5-7a and β-L5-7a Graphyne Polymorphic Varieties

Calculations of the structural and energy parameters, band structure and density of electronic states of new structural varieties of graphyne have been performed by the density functional theory method. The initial structure of the nine polymorphs was theoretically constructed on the basis of the 5-7a graphene layer. As a result of the calculations, the structure of only five graphyne layers was found to be stable: α-L5-7a, β1-L5-7a, β2-L5-7a, β3-L5-7a and β4-L5-7a. The structure of layers γ1-L5-7a, γ2-L5-7a, and γ3-L5-7a is transformed into the structure of graphene layers by geometric optimization, and the graphyne layer γ4-L5-7a is transformed sp+sp2 layer L3-6-13. The sublimation energy of the stable graphyne polymorphs varies from 6.66 to 6.78 eV/atom. The density of electronic states at the Fermi energy level for all α-L5-7a and β-L5-7a layers of graphyne is different from zero, so the new graphyne polymorphs should have metallic properties.

Theoretical Research on Structure and Infrared Spectra of the 9-Methacrylate Carbazole Molecule

Using the quantum chemical density functional theory method in the Gaussian03W package, the spatial configuration of this compound is optimized by using B3LYP/6-31G(d) as the base group, in which the data of bond length, bond angle and spatial dihedral angle of the compound molecule are obtained. Based on the optimized stable structure, the infrared vibration frequency of the molecule is calculated, and the infrared spectrum is drawn. There is no imaginary frequency in the calculation results of frequency value, which indicates that the optimized configuration of 9-methacryloyl carbazole molecule is reasonable, and the peak position of infrared spectrum is assigned.

SIMULATION OF POLYMORPHIC VARIETIES OF HEXAGONAL GRAPHENE FUNCTIONALIZED BY HYDROXYL GROUPS

Моделирование кристаллической и электронной структуры слоев гексагонального графена, на поверхность которых были химически адсорбированы гидроксильные группы, было выполнено методом теории функционала плотности. В результате расчетов была установлена возможность устойчивого существования пяти структурных разновидностей COH - L слоев. Слоевая плотность изменяется от 1,62 до 1,72 мг/м. Длина водород-кислородной связи варьируется в диапазоне от 1,046 до 1,079 Å, а углерод-кислородной связи - от 1,455 до 1,465 Å. Ориентация O - H связей относительно плоскости слоев может варьироваться в зависимости от выбора элементарной ячейки слоя. Минимальной энергией сублимации и равной 18,69 эВ/(COH) обладает слой COH-L - T4, а максимальную энергию сублимации 18,93 эВ/(COH) имеет слой COH - L - T1. Электронная структура всех COH слоев характеризуется наличием прямой запрещенной зоны на уровне энергии Ферми, изменяющейся в диапазоне от 3,02 до 4,56 эВ. Computer simulation of the crystal and electronic structure of hexagonal graphene layers, on the surface of which hydroxyl groups, chemically adsorbed, was performed by the density functional theory method. As a result of calculations, the possibility of the stable existence of five structural varieties of COH - L layers was established. The layer density varies from 1,62 to 1,72 mg/m. The length of the hydrogen-oxygen bond varies in the range from 1,046 to 1,079 Å, and the carbon-oxygen bond-from 1,455 to 1,465 Å. The orientation of the -OH bonds relative to the surface of the layers can vary depending on the choice of the unit cell of the layer. Layer COH - L - T4 has the minimum sublimation energy equal to 18,69 eV/(COH), and layer COH - L - T1 has the maximum sublimation energy 18,93 eV/(COH). The electronic structure of all COH layers is characterized by the presence of a direct band gap at the Fermi energy level, varying in the range from 3,02 to 4,56 eV.

FORMATION OF A NOVEL DIAMOND-LIKg BILAYER BASED ON 5-7 GRAPHENE

Выполнены первопринципные расчеты структуры и свойств орторомбического графена L и нового алмазоподобного бислоя, формируемого на его основе. Расчеты методом теории функционала плотности показали, что графен L, состоящий из топологических дефектов Стоуна-Уэльса, должен устойчиво существовать при нормальных условиях, и его структура должна волнообразно гофрироваться. При сильном одноосном сжатии бислойного графена L может происходить формирование нового алмазоподобного бислоя DL. Давление фазового перехода «L → DL» составляет 10,1 ГПа, когда межслоевое расстояние в бислойном графене уменьшается до 1,61 Å. Этот бислой имеет орторомбическую кристаллическую решетку (pbam) с параметрами a = 10,145 Å и b = 5,270 А. Элементарная ячейка бислоя DL pbam содержит 32 атома углерода. Длины связей изменяются в интервале от 1,5590 до 1,6226 Å, тогда как углы между связями принимают значения от 89,62 до 140,8°. Структура алмазоподобного бислоя должна быть стабильна до 270 К. Рассчитанные значения поверхностной плотности и разностной полной энергии этого бислоя относительно полной энергии алмаза равны 1,19·10 г/см и 1,31 эВ/атом, соответственно. Бислой DL pbam должен быть полупроводником с шириной прямой запрещенной зоны 1,63 эВ. Irst-principle calculations of the structure and properties of orthorhombic L graphene and a novel diamond-like bilayer formed on its basis are performed. The calculations using the density functional theory method showed that L- graphene of Stone-Wales defects should exist stably under normal conditions, and its structure should be corrugated in a wave-like manner. Under strong uniaxial compression of bilayer L graphene, the formation of the novel diamond-like DL bilayer can occur. The pressure of the « L → DL» phase transition is 10,1 GPa, when the interlayer distance in bilayer graphene decreases to 1,61 Å. This bilayer has an orthorhombic crystal lattice (pbam) with the parameters a = 10,145 Å and b = 5,270 Å. The unit cell of the DL- pbam bilayer contains 32 carbon atoms. The bond lengths vary in the range from 1,5590 to 1,6226 Å, while the angles between these bonds range from 89,62 to 140,8°. The structure of the diamond-like bilayer should be stable up to 270 K. The calculated values of the surface density and the difference total energy of this bilayer relative to the diamond total energy are 1,19 -10 g/cm and 1,31 eV/atom, respectively. The DL pbam bilayer should be a semiconductor with a straight bandgap of 1,63 eV.

Study on the adsorption of 2,4-dichlorophenoxyacetic acid on carbon nanotube by means of density functional theory

The adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on the catalytic systems comprising a transition metal (Fe, Ag) on a single walled carbon nanotube (CNT) has been investigated using density functional theory method. The adsorption energy, charges on atoms, bond orders have been calculated and analysed. The obtained results indicate that the adsorption of 2,4-D on the pristine CNT is physical of nature. Metal atoms can easily be doped on CNT due to the formation of chemical bonds. The M-CNT systems (M = Fe, Ag) have the ability to chemically adsorb 2,4-D. The results have also shown that the Fe-CNT is more effective at adsorbing 2,4-D as compare to the Ag-CNT.

Theoretical Inspection of TM-P4C Single-Atom Electrocatalyst: Ultra-High Performance for bifunctional Oxygen Reduction and Evolution Reactions

Developing the cost-effective or even bifunctional electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with industrially relevant activity is highly desired for metal-air batteries at the current stage. Herein, in this work, the catalytic performances of the single transition metal (TM) atom embeds graphene sheet with the tetra-coordinates Phosphorus (TMP4) for ORR and OER were investigated based on the density functional theory method. The results demonstrate that the most promising ORR and OER catalytic activity can achieved on the CoP4 with the smallest potential gap ∆E and the lowest overpotentials of 0.37 and 0.32 eV among all TMP4 systems, respectively, and the catalytic activity is even better than that of the traditional Pt and IrO2 catalysts. Furthermore, the AIMD calculation was conducted to confirm the thermodynamics stability of CoP4. This work screens out promising candidates for novel graphene-based bifunctional ORR and OER catalysts and provides the theoretical guidance for the development of single-atom catalysts.

New polymorphic varieties of boron nitride with graphene-like structures

First-principle calculations of the structure and electronic properties of four new polymorphic varieties of graphene-like boron nitride, the structure of which is similar to the structure of graphene polymorphs, the atoms in which are in the spirit of different structural positions, were performed by the density functional theory method in the generalized gradient approximation. As a result of the studies carried out, the possibility of stable existence of three monoatomic boron nitride layers: BN-L4-6-8a, BN-L4-6-8b and BN-L4-10 has been established. The BN-L4-12 layer is transformed into the BN-L4-6-8 layer during geometric optimization. The lengths of interatomic bonds in boron nitride monolayers vary in the range 1.4353 Å ÷ 1.4864 Å, and the bond angles in the range 84.05° ÷ 152.26°. The band gap of the BN layers varies from 3.16 eV to 3.90 eV. Sublimation energies are in the range from 16.67 eV/(BN) to 17.61 eV/(BN).

Can the Antivirals Remdesivir and Favipiravir Work Better Jointly? In Silico Insights

The proverb “Old is gold” is applicable in drug discovery and the proverb “All that Glitters is not Gold” is also appropriate. In the COVID-19 era, there has been a race for drugs to be effective against SARS-CoV-2. There are reports about the uses of Remdesivir and Favipiravir as existing antivirals against virus but none have been conclusive so far. In the attempts for innovations, the combination of drugs is also under trials. Therefore, we used the density functional theory method and quantum theory of atoms in molecules to investigate drug-drug interactions involving Remdesivir and Favipiravir. The computed parameters were related to the antiviral actions of both drugs together. The results indicate enhanced antiviral activity and it will be worthy to consider additional investigations with the combination of these two drugs.