Density functional theory and molecular dynamics simulation study on corrosion inhibition performance of mild steel by mercapto-quinoline Schiff base corrosion inhibitor

Corrosion inhibition mechanism of two mercapto-quinoline Schiff bases, eg., 3-((phenylimino)methyl)quinoline-2-thiol (PMQ) and 3-((5-methylthiazol-2-ylimino)methyl) quinoline-2-thiol (MMQT) on mild steel surface is investigated by quantum chemical calculation and molecular dynamics simulation. Quantum chemical parameters such as E_HOMO, E_LUMO, energy gap (ΔE), dipolemoment (µ), electronegativity (χ), global hardness (η) and fraction of electron transfers from the inhibitor molecule to the metallic atom surface (ΔN) have been studied to investigate their relative corrosion inhibition performance. Parameters like local reactive sites of the present molecule have been analyzed through Fukui indices. Moreover, adsorption behavior of the inhibitor molecules on Fe (1 1 0) surface have been analyzed using molecular dynamics simulation. The binding strength of the concerned inhibitor molecules on mild steel surface follows the order MMQT>PMQ, which is in good agreement with the experimentally determined inhibition efficiencies. In view of the above, our approach will be helpful for quick prediction of a potential inhibitor from a lot of similar inhibitors and subsequently in their rational designed synthesis for corrosion inhibition application following a wet chemical synthetic route.     

Study of reduction processes over cerium oxide surfaces with atomic hydrogen using ultra accelerated quantum chemical molecular dynamics

Ceria plays an important role in catalysis, due to its ability to store and release oxygen depending on the condition present in the catalyst environment. To analyze the role of ceria in catalytic reactions, it is necessary to know the details of the interaction of ceria surface with environmentally sensitive molecules. This study was conducted using ultra accelerated quantum chemical molecular dynamics. Its purpose was to investigate the reduction process of the (1 1 1) and (1 1 0) surfaces of ceria with atomic hydrogen as well as water desorption mechanisms from the surfaces. This simulation demonstrated that when a high-energy colliding hydrogen atoms are adsorbed on the ceria, it pulls up an O atom from the ceria surfaces and results in the formation of a H₂O molecule. This is the first dynamics simulation related to such reduction processes based on quantum chemistry.     

Conformational lability of ibuprofen in supercritical carbon dioxide

A study of conformational equilibria of ibuprofen in vacuum and supercritical carbon dioxide (SC CO₂) was carried out using methods of quantum chemistry and molecular dynamics simulation. It was found that ibuprofen forms 12 different conformations in SC CO₂, two of them correspond to the structure of the molecule in the crystal lattice of the first and second polymorph. It was shown that the GAFF force field allows one to obtain the characteristics of conformers, almost coinciding with those obtained by quantum chemical calculations at the B3LYP/cc-pVTZ level of theory.     

First-principles study of dissociation processes of O2 molecular on the Al (111) surface

The trajectories of adsorption and dissociation process of O₂ on the Al (111) surface were studied by the spin-polarized ab initio molecular dynamics method, and the adsorption activation energy was clarified by the NEB method with hybrid functionals. Three typical dissociation trajectories were found through simulation of O₂ molecule at different initial positions. When vertically approaches to the Al surface, the O₂ molecule tends to rotate, and the activation energy is 0.66eV. If O₂ molecule does not rotate, the activation energy will increase to 1.43 eV, and it makes the O atom enter the Al sublayer eventually. When the O₂ molecules parallel approach to the Al surface, there is no activation energy, due to the huge energy released during the adsorption process.     

Effects of surface corrugation on the molecular rotational dependence of H2 dissociative adsorption dynamics on Cu(100)

We investigate and discuss how surface corrugation affects the molecular rotational dependence of H₂ dissociative adsorption dynamics on Cu(100) by performing six-dimensional (6D) quantum dynamics calculations. We calculate the dissociative adsorption probability as a function of the initial rotational state J and the normal energy E_norm of incident molecules, and compare with the dissociative adsorption results obtained by four-dimensional (4D) quantum dynamics calculations where the surface is treated as flat. In our calculation, for the case of normal incidence, the increase in dissociative adsorption probability with increasing E_norm and the non-monotonic behavior of dissociative adsorption probability with respect to J are suppressed on a corrugated surface as compared to that on a flat surface.     

Methane molecule over the defected and rippled graphene sheet

Adsorption of a methane molecule (CH₄) onto a defected and rippled graphene sheet is studied using ab initio and molecular mechanics calculations. The optimal adsorption position and orientation of this molecule on the graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined and the adsorption energies are calculated. In light of the density of states, we used the SIESTA code. It is found that (i) classical force field yields adsorption energy comparable with experimental result and ab initio calculation; (ii) the periodic nature of the van der Waals potential energy stored between methane and perfect sheet is altered due to the insertion vacancies and sinusoidal ripples; (iii) the van der Waals potential energy is found to be sensitive to the presence of the vacancies and the ripples so that the added molecule avoids to be around vacant cites and on top of the peaks.     

Hydrogen and deuterium adsorption on uranium decorated graphene nanosheets: A combined molecular dynamics and density functional theory study

In this study, the combined density functional theory (DFT) and molecular dynamics (MD) simulation methods were carried out to investigate the potential capability of uranium-decorated graphene (U–G) for the separation of deuterium from hydrogen gases. Graphene with hexagonal honeycomb lattice arrangement is suitable for adsorption of individual uranium atoms, with a high binding energy (?1.173 eV) and U-U distance longer than 7 Å. This U-G system has ability to hold up to six H₂ (5.16% wt) or seven D₂ (11.75% wt) molecules per U atoms. To gain further insights into these interactions, partial electronic density of states (PDOS) and the electron density distribution of the elements were analyzed. The MD results are in reasonable agreement with the results obtained by DFT method. Our calculated results indicate that at room temperature, D₂ molecule has higher affinity for U-G system than the H₂ molecule. In order to increase the D₂ separation factor from H₂, the effect of temperature was studied. The results indicated that adsorption ratio of D₂ to H₂ increases by decreasing the temperature.     

C2H2在金刚石（001）-（2×1）重构面上吸附的分子动力学模拟

利用Brenner半经验多体相互作用势和分子动力学模拟方法，研究了乙块（C₂H₂）分子在金刚石（001）-（2×1）重构表面上的碰撞动力学过程与化学吸附构型的关系.观察到C₂H₂在金刚石表面的6种吸附结构.约95％的吸附呈C₂H₂与表面形成两个σ单键的形式.讨论了轰击能量、入射位置及金刚石表面原子的空间位形对各种吸附构型形成的影响.还给出了化学吸附过程的分子快照，并讨论了C₂H₂分子与表面的能量交换关系. 关键词：     

Inhibition performance of 2-mercaptobenzothiazole derivatives in CO2 saturated solution and its adsorption behavior at Fe surface

Two 2-mercaptobenzothiazole derivatives, N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-dodecylamine (BTBMDA) and N,N′-bis-(2-thionobenzothiazolin-3-yl-methyl)-n-octadecylamine (BTBMOA), were synthesized under microwave irradiation. Their inhibition performance for N80 steel in CO₂ saturated solution at 90 °C were tested by weight loss method and the surface analysis was performed by SEM. The adsorption behavior of two inhibitors at the Fe surface was studied by the molecular dynamics simulation method and the quantum chemistry calculations. Results showed that the two inhibitors could inhibit the corrosion of N80 steel in simulated solution significantly. There were two types of end configurations for two inhibitors at the Fe surface in the molecular dynamics simulation, and the two inhibitors adsorbed at the surface mainly through one of the two types.     

Vibrational spectrum at a water surface: a hybrid quantum mechanics/molecular mechanics molecular dynamics approach

A hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulation is applied to the calculation of surface orientational structure and vibrational spectrum (second-order nonlinear susceptibility) at the vapor/water interface for the first time. The surface orientational structure of the QM water molecules is consistent with the previous MD studies, and the calculated susceptibility reproduces the experimentally reported one, supporting the previous results using the classical force field MD simulation. The present QM/MM MD simulation also demonstrates that the positive sign of the imaginary part of the second-order nonlinear susceptibility at the lower hydrogen bonding OH frequency region originates not from individual molecular orientational structure, but from cooperative electronic structure through the hydrogen bonding network.     

未燃尽炭表面吸附汞的机理研究

本文应用量子化学密度泛函理论B3PW91方法,在lanl2dz基组水平上研究了飞灰中未燃尽炭表面对汞的微观吸附机理.建立了表征未燃尽炭的饱和簇模型,讨论了该簇模型在不同的情况下对汞的吸附作用,计算得出吸附能,并做出了相关的实验解释.结果表明量子化学的理论计算是揭示汞等痕量元素的吸附机理以及筛选合适吸附剂的一种有效方法.     

Theoretical investigations of pyridine derivatives as potential high energy density materials

Density function theory has been employed to study pyridine derivatives at the B3LYP/6‐31 G(d,p) and B3P86/6‐31 G(d,p) levels. The crystal structures were obtained by molecular mechanics methods. The heats of formation (HOFs) were predicted based on the isodesmic reactions. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and HOFs. The thermal stability of the title compounds was investigated by the bond dissociation energies and the energy gaps (ΔE_LUMO?HOMO) predicted. It is found that there are good linear relationships between detonation velocity, detonation pressure, and the number of nitro group. The simulation results reveal that molecule G performs similar to the famous explosive HMX and molecule D outperforms HMX. According to the quantitative standard of energetics and stability as high energy density materials, molecule D essentially satisfies this requirement. These results provide basic information for molecular design of novel high energetic density materials. Copyright © 2012 John Wiley & Sons, Ltd.     

Interaction mechanism between copolymer inhibitor and β-dicalcium silicate surface based on molecular dynamics simulation

Copolymer inhibitor with multifunctional groups has a good effect on inhibiting the secondary reaction in the clinker leaching process for alumina production, but the inhibition mechanism of the copolymer is not clear yet. In this paper, molecular dynamics simulation was used to study the adsorption process of the copolymer inhibitor with multifunctional groups, such as acrylic acid-vinyl alcohol copolymer (PAV) and acrylic acid-hydroxypropyl acrylate copolymer (PAH), on the β-dicalcium silicate (C₂S) crystal surface, and reveal its inhibiting mechanism. Meanwhile, the polyacrylic acid (PAA) with only the carboxyl group also is simulated for comparing the inhibition effect with copolymer inhibitors. The results show that the binding energy between copolymer (PAV, PAH) and β-C₂S is greater than that of PAA with a single functional group. The order of binding energy is as follows: PAH?>?PAV?>?PAA. In aqueous solution, the water molecule can restrict the degree of deformation of polymers, increase the distance between polymers and β-C₂S and then lead to weakening of the adsorption of polymers on the crystal surface. The comprehensive and coordination effect of carboxyl and hydroxyl functional groups in PAV and PAH can strengthen the adsorption of copolymers on the β-C₂S surface. The different spatial distribution of multifunctional groups in the molecular structure has a different influence on the adsorption of the copolymer. The results can provide a theoretical basis for researching new and highly effective copolymer inhibitors with multifunctional groups.

Compared the adsorption state: The comprehensive and coordinate action of carboxyl and hydroxyl groups of the inhibitor with multifunctional groups make the inhibitor have a stronger adsorption ability on the surface of β-C₂S than that with a single functional group. The results obtained in this paper can provide a theoretical basis for the research and development of new and highly effective polymeric inhibitors with multifunctional groups.

Highlights

The interaction between copolymer and β-C₂S was investigated by MD simulation.

The binding energy order between polymers and β-C₂S is PAH?>?PAV?>?PAA.

The presence of water molecules can weaken the adsorption of the copolymer on the surface of β-C₂S.

The comprehensive and coordinate action of carboxyl and hydroxyl groups of the inhibitor with multifunctional groups make the inhibitor have a stronger adsorption ability on the surface of β-C₂S than that with a single functional group.     

Nuclear spin-spin coupling constants prediction based on XGBoost and LightGBM algorithms

Nuclear magnetic resonance (NMR) is a robust method for the analysis of molecular complex structures, and the measurement of the nuclear spin–spin coupling constant is the key. In this paper, based on the 3D coordinates of the atoms in the molecule, the spin–spin coupling constants of atom-pairs are directly predicted using Extreme Gradient Boosting (XGBoost) and Light Gradient Boosting Machine (LightGBM). The calculated result of DFT method is taken as the target value. Experiment shows that LightGBM (R²: 0.93) overall performance is better than XGBoost. In some molecules, the predicted fit (R²) of the coupling constant between atoms even reached 1.00. This research avoids complex quantum mechanics and can assist in NMR to gain insight into the structure and dynamics of molecules, thereby enriching the data information analysis method of nuclear magnetic interaction.     

Investigation of the interaction of some astrobiological molecules with the surface of a graphite (0 0 0 1) substrate. Application to the CO, HCN, H2O and H2CO molecules

Detailed interaction potential energy calculations are performed to determine the potential energy surface experienced by the molecules CO, HCN, H₂O and H₂CO, when adsorbed on the basal plane (0 0 0 1) of graphite at low temperatures. The potential energy surface is used to find the equilibrium site and configuration of a molecule on the surface and its corresponding adsorption energy. The diffusion constant associated with molecular surface diffusion is calculated for each molecule.     

Hydrogen oxidation and proton transport at the Ni–zirconia interface in solid oxide fuel cell anodes: Quantum chemical predictions

We explore the hydrogen anode reaction chemistry at the Ni–zirconia triple phase boundary in solid oxide fuel cells by using hybrid density functional quantum chemistry calculations and cluster models. The activation energy for H spillover is calculated to be the same order of magnitude as experimental estimates at the reversible potential. Proton transport on the oxide surface is shown to be activated by strongly held hydrogen-bonded water molecules: in the absence of H₂O the activation energy is calculated to be 4.98 eV and the water molecule reduces the activation energy to 0.25 eV. Substitutional Y³⁺ (for Zr⁴⁺) is shown to slow proton diffusion when present in the zirconia surface.     

基于深度张量神经网络预测有机分子的相互作用能

分子的相互作用在分子动力学模拟过程中起着关键的作用. 受限于计算资源,大分子的长时间尺度的相互作用能无法通过量化计算实现. 本文采用一种深度学习框架-深度张量神经网络来预测三个有机分子相关体系中量化精度的相互作用能. 其中,分子的几何结构和原子类型作为网络的输入用于预测相互作用能. 通过分层生成的数据集合实现了网络中隐层参数的优化和训练. 相互作用能的预测结果显示,深度张量神经网络可以在较短的时间内,在1 kcal/mol的平均绝对误差的范围内准确预测分子间的相互作用能. 这一过程提高了计算效率,并为计算相互作用能提供了可靠的计算框架.     

Electrochemical and theoretical investigation on the corrosion of aluminium in acidic solution containing some Schiff bases

The effect of newly synthesised three Schiff bases—2-[2-aza-2-(5-methyl(2-pyridly))vinyl]phenol, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]-4-bromophenol, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]-4-chlorophenol—on the corrosion behaviour of aluminium in 0.1 M HCl were investigated using potentiodynamic polarisation, electrochemical impedance spectroscopy and linear polarisation methods. Polarisation curves indicate that all studied Schiff bases were acting as mixed type inhibitors. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on aluminium surface. Adsorption of these inhibitors follows Langmuir adsorption isotherm. Thermodynamic parameters of adsorption (K_ads, ΔG_ads) of studied Schiff bases were calculated using Langmuir adsorption isotherm. The variation in inhibition efficiency values depends on the type of functional groups substituted on benzene ring. It was found that the presence of bromine and chlorine atoms in the molecular structure of studied Schiff bases facilitate the adsorption of molecule on aluminium surface.The correlation between the inhibition efficiencies of studied Schiff bases and their molecular structure has been investigated using quantum chemical parameters obtained by MNDO semi-empirical SCF-MO methods. These results indicate that adsorption of studied Schiff bases depends on the charge density of adsorption centres and dipole moments.     

Theoretical study on collision dynamics of H+ + H2O at low energies

Scattering dynamics of a water molecule in collision with proton is studied based on a time-dependent density functional theory and coupled with the molecular dynamics method, in which the electrons are described by quantum mechanics and the nuclei are described by classical mechanics. Four different incident directions at 46 eV are chosen in order to investigate the orientations effect, and the energy-dependent effect in low energy region is explored under impact energies 27, 36 and 46 eV. Reaction channels, scattering angles and energy loss of protons are calculated. The differences between those characteristics are unobvious in large impact parameters, which are irrespective of the incident orientations due to weak projectile-target interaction. In small impact parameters, the results strongly depend on the collision energy and orientation.