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NMR spectroscopy has become a standard technique in studies both on carbon capture and storage. 13C NMR allows the detection of two peaks for carbonated aqueous samples: one for CO2(aq) and another one for the species H2CO3, HCO3−, and CO32−—herein collectively named HxCO3x‐2. The chemical shift of this second peak depends on the molar fraction of the three species in equilibrium and has been used to assess the equilibrium between HCO3− and CO32−. The detection of H2CO3 at low pH solutions is hindered, because of the concurrent liberation of CO2 when the medium is acidified. Herein, a valved NMR tube facilitates the detection of the HxCO3x‐2 peak across a wide pH range, even at pH 1.8 where the dominant species is H2CO3. The method employed the formation of frozen layers of NaH13CO3 and acid solutions within the tube, which are mixed as the tube reaches room temperature. At this point, the tube is already securely sealed, preventing any loss of CO2 to the atmosphere. A spectrophotometry approach allowed the measurement of the actual pH inside the pressurized NMR tube. The chemical shift for H2CO3 was determined as 160.33 ± 0.03 ppm, which is in good agreement with value obtained by DFT calculations combined with Car–Parrinello molecular dynamics. The H2CO3 pKa value determined by the present method was 3.41 ± 0.03, for 15% D2O aqueous medium and 0.8 mol/L ionic strength. The proposed method can be extended to studies about analogs such as alkyl carbonic and carbamic acids. [ABSTRACT FROM AUTHOR]

Silicon, traditionally known as an indirect band gap semiconductor, unveils intriguing properties at the nanoscale, stemming from deviations from k-conservation rules within nanostructures. In our study, we scrutinized four hydrogenated Si 0D-nanostructures—Si10H16, Si14H20, Si18H24, and Si22H28—to unravel their dynamic stability under thermal fluctuations and optical characteristics. We initiated our exploration by employing the TD-DFT framework to generate and analyze the optical properties of these geometrically optimized nanostructures. Simultaneously, we conducted ab initio molecular dynamics simulations to examine the structural robustness and thermal stability of the four structures. Leveraging the Car-Parrinello molecular dynamics approach within the Quantum ESPRESSO open software suite, we observed temperature evolution and stability differences among the nanostructures at targeted temperatures 40 and 300 K. Our subsequent investigation delved into the Turbo-Lanczos time-dependent DFT method, unraveling the optical properties and excited-state dynamics of hydrogenated Si nanostructures. The results unveiled shifts towards higher energy absorption edges E0, accompanied by alterations in the permittivity tensor, complex refractive index, oscillator strength, and reflectivity. Notably, the analysis revealed an enlarged HOMO-LUMO gap, distinctive from bulk Si. Furthermore, our models predicted the elimination of phase-dependent E1/E2 optical transition peaks in the imaginary part of the dielectric function, and a gradual decrease in the low-frequency dielectric response with increased hydrogenation of the amorphous structures. These findings underscore the promising applications of hydrogenating Si nanostructures in diverse technological domains such as optoelectronics, memristors, sensors, and quantum computing. Their tunable optical properties, size-dependent behaviors, and compatibility with existing silicon-based devices make them particularly appealing for next-generation technologies.

The concept of classical nuclear motion is extremely successful in describing motion at the atomic scale. In describing chemical reactions, it is even far more convincing than the picture obtained by using the Schrödinger equation for time development. However, this theory must be subject to critical tests. In particular, it must be checked if vibrational and rotational spectra are obtained correctly. Particularly critical are the spectra of small molecules containing the light hydrogen atom, since they have a distinctive rotational structure. The present study presents computations of the spectra of ammonia and hydrogen chloride using ab initio molecular dynamics, that is, by describing nuclear motion classically.

The assumption that nuclear motion is classical explains many phenomena. The problems of Schrödinger's cat and the EPR paradoxon do not exist in a perfectly deterministic theory. All it needs is to describe nuclear motion classically right from the beginning. To establish this simple idea, it must be tested for as many examples as possible. In the present paper, we use ab initio molecular dynamics to investigate the infrared spectrum of a 'magic' protonated water cluster H 3 O + (H 2 O) 20 which exhibits some features that were believed to afford a quantum treatment of nuclear motion. The role of the temperature in contrast to a quantum mechanical description is discussed. [ABSTRACT FROM AUTHOR]

The non-orthogonal local submatrix method applied to electronic structure–based molecular dynamics simulations is shown to exceed 1.1 EFLOP/s in FP16/FP32-mixed floating-point arithmetic when using 4400 NVIDIA A100 GPUs of the Perlmutter system. This is enabled by a modification of the original method that pushes the sustained fraction of the peak performance to about 80%. Example calculations are performed for SARS-CoV-2 spike proteins with up to 83 million atoms. [ABSTRACT FROM AUTHOR]

(CF3)2CFCN with excellent insulation performance has been proposed to replace the traditional SF6 as a new insulating medium in power equipment. In the present study, the molecular structure and radiative efficiency (RE) of (CF3)2CFCN are calculated and compared with SF6 based on density‐functional theory (DFT) calculation. The decomposition of pure (CF3)2CFCN and the basic interactions between (CF3)2CFCN and hydroxyl radical in the constructed co‐crystal of (CF3)2CFCN‐H2O have been simulated by applying Monte‐Carlo calculation and Car–Parrinello molecular dynamics method, in order to obtain reasonable and full‐scale atmospheric dissociation processes. Then the detailed decomposition pathways are learned with DFT method of M06‐2X. The rate constants of different pathways are further applied for calculating the atmosphere lifetime of (CF3)2CFCN, to evaluate the possibility of applying it as an alternative gas of SF6 in power equipment. All the atmospheric chemical behaviors are determined by electronic structure and reflected by the decomposition pathways of (CF3)2CFCN with interacting with hydroxyl radicals. Rather than traditional hypothesizing reaction models given by the chemical intuitions, this study provides a new view angle to understand the dissociation pathways based on first‐principle molecular dynamic method, and to evaluate the atmospheric chemical behaviors of other protective gas of power equipment. [ABSTRACT FROM AUTHOR]

The concept of classical nuclear motion is extremely successful in describing motion at the atomic scale. In describing chemical reactions, it is even far more convincing than the picture obtained by using the Schrödinger equation for time development. However, this theory must be subject to critical tests. In particular, it must be checked if vibrational and rotational spectra are obtained correctly. Particularly critical are the spectra of small molecules containing the light hydrogen atom, since they have a distinctive rotational structure. The present study presents computations of the spectra of ammonia and hydrogen chloride using ab initio molecular dynamics, that is, by describing nuclear motion classically. [ABSTRACT FROM AUTHOR]

Ab initio molecular dynamics combines a classical description of nuclear motion with a density-functional description of the electronic cloud. This approach nicely describes chemical reactions. A possible conclusion is that a quantum mechanical description of nuclear motion is not needed. Using Occam’s razor, this means that, being the simpler approach, classical nuclear motion is preferable. In this paper, it is claimed that nuclear motion is classical, and this hypothesis will be tested in comparison to methods with quantum mechanical nuclear motion. In particular, we apply ab initio molecular dynamics to two photoreactions involving hydrogen. Hydrogen, as the lightest element, is often assumed to show quantum mechanical tunneling. We will see that the classical picture is fully sufficient. The quantum mechanical view leads to phenomena that are difficult to understand, such as the entanglement of nuclear motion. In contrast, it is easy to understand the simple classical picture which assumes that nuclear motion is steady and uniform unless a force is acting. Of course, such a hypothesis must be verified for many systems and phenomena, and this paper is one more step in this direction.

Ab initio molecular dynamics combines a classical description of nuclear motion with a density-functional description of the electronic cloud. This approach nicely describes chemical reactions. A possible conclusion is that a quantum mechanical description of nuclear motion is not needed. Using Occam's razor, this means that, being the simpler approach, classical nuclear motion is preferable. In this paper, it is claimed that nuclear motion is classical, and this hypothesis will be tested in comparison to methods with quantum mechanical nuclear motion. In particular, we apply ab initio molecular dynamics to two photoreactions involving hydrogen. Hydrogen, as the lightest element, is often assumed to show quantum mechanical tunneling. We will see that the classical picture is fully sufficient. The quantum mechanical view leads to phenomena that are difficult to understand, such as the entanglement of nuclear motion. In contrast, it is easy to understand the simple classical picture which assumes that nuclear motion is steady and uniform unless a force is acting. Of course, such a hypothesis must be verified for many systems and phenomena, and this paper is one more step in this direction. [ABSTRACT FROM AUTHOR]

The reaction of molecular nitrogen with molecular hydrogen was simulated using ab initio molecular dynamics. The reaction was catalyzed by the addition of bulk lithium and oxygen. As is known from the experiment, the limiting step is the breaking of the nitrogen–nitrogen triple bond. We observed a mechanism that has not been discussed before: one of the nitrogen atoms of a nitrogen molecule is absorbed by the lithium bulk, whereas the other nitrogen atom reacts with hydrogen. Adding oxygen leads to a dominating reaction of oxygen with the lithium surface. The oxygen molecules break easily into single atoms and are, in part, absorbed by the lithium structure. Part of them remains on the surface and reacts with hydrogen. In this way, hydrogen is activated and can, in turn, react easily with molecular nitrogen. The overall reactivity as observed in the ab initio simulations reflects the extremely low density of lithium. Interstitial sites are readily occupied, leading to oxide and nitride structures.

The assumption that nuclear motion is classical explains many phenomena. The problems of Schrödinger’s cat and the EPR paradoxon do not exist in a perfectly deterministic theory. All it needs is to describe nuclear motion classically right from the beginning. To establish this simple idea, it must be tested for as many examples as possible. In the present paper, we use ab initio molecular dynamics to investigate the infrared spectrum of a ‘magic’ protonated water cluster H3O+(H2O)20 which exhibits some features that were believed to afford a quantum treatment of nuclear motion. The role of the temperature in contrast to a quantum mechanical description is discussed.

The reaction of molecular nitrogen with molecular hydrogen was simulated using ab initio molecular dynamics. The reaction was catalyzed by the addition of bulk lithium and oxygen. As is known from the experiment, the limiting step is the breaking of the nitrogen–nitrogen triple bond. We observed a mechanism that has not been discussed before: one of the nitrogen atoms of a nitrogen molecule is absorbed by the lithium bulk, whereas the other nitrogen atom reacts with hydrogen. Adding oxygen leads to a dominating reaction of oxygen with the lithium surface. The oxygen molecules break easily into single atoms and are, in part, absorbed by the lithium structure. Part of them remains on the surface and reacts with hydrogen. In this way, hydrogen is activated and can, in turn, react easily with molecular nitrogen. The overall reactivity as observed in the ab initio simulations reflects the extremely low density of lithium. Interstitial sites are readily occupied, leading to oxide and nitride structures. [ABSTRACT FROM AUTHOR]

Nanoporous membranes promise energy-efficient water desalination. Hexagonal boron nitride (h-BN), like graphene, exhibits outstanding physical and chemical properties, making it a promising candidate for water treatment. We employed Car-Parrinello molecular dynamics simulations to establish an accurate modeling of Na + and Cl - permeation through hydrogen passivated nanopores in graphene and h-BN membranes. We demonstrate that ion separation works well for the h-BN system by imposing a barrier of 0.13 eV and 0.24 eV for Na + and Cl - permeation, respectively. In contrast, for permeation of the graphene nanopore, the Cl - ion faces a minimum of energy of 0.68 eV in the nanopore plane and is prone toward blockade of the nanopore, while the Na + ion experiences a slight minimum of 0.03 eV. Overall, the desalination performance of h-BN nanopores surpasses that of their graphene counterparts., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Is a classical description of nuclear motion sufficient when describing chemical reactions and spectra? This question is interesting because many researchers use a classical description of nuclear motion in molecular dynamics simulations. The present paper investigates some phenomena that were previously attributed to nuclear quantum effects. The question is if these phenomena can be modeled with traditional Car–Parrinello molecular dynamics, that is, with a method which treats nuclear motion classically and which is widely applied to the simulation of chemical reactions and spectra. We find that for the investigated system no additional paradigm is needed for describing chemical reactions. The special reactivity observed for carbenes can be attributed to the special environment represented by a noble gas matrix and to an additional transition state that was not considered before. Also the infrared spectrum of porphycene is perfectly modeled by traditional Car–Parrinello molecular dynamics. More studies are necessary to decide to what extent classical nuclear motion can replace the quantum mechanical description. [ABSTRACT FROM AUTHOR]

Car–Parrinello molecular dynamics simulations were applied to investigate phase-transition behavior of (H 2 O) n few-body system for n=1−4 at BLYP-GGA level of density-functional theory. A number of important indicators including Lindemann index, ionic mean square displacements, radial distribution function, and shape deformation parameter were accordingly calculated as functions of temperature from 5 to 2000 K. All the four systems exhibited high thermal stabilities compared to bulk water with melting points estimated at T m = 1200 , 950 , and 700 K for n=2,3, and 4, respectively. No obvious melting behavior was also observed for n=1 due to strong O–H covalent bonds. These T m values were also found to obey a decreasing trend as the size of the system increases, showing that a minimum size value can also be estimated for which characteristics of liquid water at the thermodynamic limit would consequently appear, in case of studying larger systems with n ≫ 4. [ABSTRACT FROM AUTHOR]

To be accepted by the community, the claim that nuclear motion has to be treated classically must be tested for all kinds of phenomena. For the moment we claim that in a quantum chemical calculation, a classical description of nuclear motion is superior to the use of the Schrödinger equation, and investigate how far we get with this statement. In the present paper we address the question what nuclear quantum statistics means in this context. We will show that the Maxwell–Boltzmann velocity distribution evolves quickly in any molecular dynamics simulation and this guarantees the physically correct behavior of molecular systems. Using first‐principles molecular dynamics simulations, or more precisely Car–Parrinello molecular dynamics, we investigate what this means for Bose‐Einstein condensates and for Cooper pairs. It turns out that our approach can explain all relevant phenomena. As a consequence, we can introduce a deterministic formulation of quantum mechanics and can get rid of all the paradoxa in traditional quantum mechanics. The basic idea is to treat electrons and nuclei differently. [ABSTRACT FROM AUTHOR]

NMR spectroscopy has become a standard technique in studies both on carbon capture and storage. 13 C NMR allows the detection of two peaks for carbonated aqueous samples: one for CO 2(aq) and another one for the species H 2 CO 3 , HCO 3 - , and CO 3 2- -herein collectively named H x CO 3 x-2 . The chemical shift of this second peak depends on the molar fraction of the three species in equilibrium and has been used to assess the equilibrium between HCO 3 - and CO 3 2- . The detection of H 2 CO 3 at low pH solutions is hindered, because of the concurrent liberation of CO 2 when the medium is acidified. Herein, a valved NMR tube facilitates the detection of the H x CO 3 x-2 peak across a wide pH range, even at pH 1.8 where the dominant species is H 2 was determined as 160.33 ± 0.03 ppm, which is in good agreement with value obtained by DFT calculations combined with Car-Parrinello molecular dynamics. The H 3 . The method employed the formation of frozen layers of NaH 13 CO 3 and acid solutions within the tube, which are mixed as the tube reaches room temperature. At this point, the tube is already securely sealed, preventing any loss of CO 2 to the atmosphere. A spectrophotometry approach allowed the measurement of the actual pH inside the pressurized NMR tube. The chemical shift for H 2 CO 3 was determined as 160.33 ± 0.03 ppm, which is in good agreement with value obtained by DFT calculations combined with Car-Parrinello molecular dynamics. The H 2 CO 3 pK a value determined by the present method was 3.41 ± 0.03, for 15% D 2 O aqueous medium and 0.8 mol/L ionic strength. The proposed method can be extended to studies about analogs such as alkyl carbonic and carbamic acids., (© 2024 John Wiley & Sons Ltd.)

We demonstrate how to fully ascribe Raman peaks simulated using ab initio molecular dynamics to specific vibrations in the structure at finite temperatures by means of Wannier functions. Here, we adopt our newly introduced method for the simulation of the Raman spectra in which the total polarizability of the system is expressed as a sum over Wannier polarizabilities. The assignment is then based on the calculation of partial Raman activities arising from self- and/or cross-correlations between different types of Wannier functions in the system. Different types of Wannier functions can be distinguished based on their spatial spread. To demonstrate the predictive power of this approach, we applied it to the case of a cyclohexane molecule in the gas phase and were able to fully assign the simulated Raman peaks.

Electrolysis is potentially a valuable tool for cleansing waste water. One might even hope that it is possible to synthesize valuable products in this way. The question is how the reaction conditions can be chosen to obtain desired compounds. In the present study we use Car–Parrinello molecular dynamics to simulate the reaction of nucleobases under electrolytic conditions. We use our own scheme (F. Hofbauer, I. Frank, Chem. Eur. J., 18, 277, 2012) for simulating the conditions after the electron transfer in a self-consistent field calculation. This scheme was employed previously to the electrolysis of pure water and of polluted solutions. On the picosecond timescale, we find a strongly different reaction behavior for each of the four nucleobases contained in DNA.

The impact of condensed‐phase and finite‐temperature effects on the theoretical X‐ray absorption spectra of transition metal complexes is assessed. The former are included in terms of the all‐electron Gaussian and augmented plane‐wave approach, whereas the latter are taken into account by extensive ensemble averaging along second‐generation Car–Parrinello ab initio molecular dynamics trajectories. We find that employing the periodic boundary conditions and including finite‐temperature effects systematically improves the agreement between our simulated X‐ray absorption spectra and experimental measurements. © 2018 Wiley Periodicals, Inc. Theoretical condensed‐phase X‐ray absorption spectra, as computed by the combined second‐generation Car–Parrinello molecular dynamics and all‐electron Gaussian and augmented plane‐wave approach, suggest that the usage of periodic boundary conditions and inclusion of finite‐temperature effects entails a systematic improvement within the X‐ray absorption fine structure range. [ABSTRACT FROM AUTHOR]

Electrolysis is a potential candidate for a quick method of wastewater cleansing. However, it is necessary to know what compounds might be formed from bioorganic matter. We want to know if there are toxic intermediates and if it is possible to influence the product formation by the variation in initial conditions. In the present study, we use Car–Parrinello molecular dynamics to simulate the fastest reaction steps under such circumstances. We investigate the behavior of amino acids and peptides under anodic conditions. Such highly reactive situations lead to chemical reactions within picoseconds, and we can model the reaction mechanisms in full detail. The role of the electric current is to discharge charged species and, hence, to produce radicals from ions. This leads to ultra-fast radical reactions in a bulk environment, which can also be seen as redox reactions as the oxidation states change. In the case of amino acids, the educts can be zwitterionic, so we also observe complex acid–base chemistry. Hence, we obtain the full spectrum of condensed-phase chemistry.

A thorough understanding of the interactions of CO 2 with the hosting porous network is crucial for the design of new adsorbent materials with enhanced gas adsorption capacity and selectivity. In this paper, first-principles molecular dynamics simulations are performed to assess the interactions of CO 2 adsorbed in a nanoporous glassy chalcogenide (i.e. chalcogel) under relevant laboratory conditions. The structure and local organization of the confined CO 2 molecules are analyzed in terms of atomic density, orientational order parameter and pair correlation functions. Maximally localized Wannier functions are used to unravel the electronic structure, the local molecular dipole and the nature of the chemical bonding at the interface between CO 2 and the glassy surface. Our results provide a useful insight on the complex interplay between the chemical interactions competing at the buried interface made by the CO 2 molecules adsorbed in g -GeS 2 chalcogel. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations and Car-Parrinello molecular dynamics (CPMD) simulations in the explicit acetonitrile-water solvent were carried out to study the ligand dissociation/exchange process and hydrogen production pathway of a common cobaloxime complex, Co(dmgH) 2 (py)Cl (py = pyridine). Our results show that the axial Cl − is readily replaced by a water molecule which is a key step for the subsequent proton transfer in the hydrogen production cycle. Moreover, the py ligand also dissociates readily from the complex at a later stage. The alternate two electrons and two protons addition pathway was identified to be the favorable one for hydrogen production. The rate determining step of the hydrogen production by Co(dmgH) 2 (py)Cl is the first protonation of the Co ion, which competes with the proton transfer to the O of the side group of the complex. [ABSTRACT FROM AUTHOR]

We present an accurate computational study of the electronic structure and lattice dynamics of solid molecular hydrogen at high pressure. The band-gap energies of the [ABSTRACT FROM AUTHOR]

Mixed quantum-classical (quantum mechanical/molecular mechanical (QM/MM)) simulations have strongly contributed to providing insights into the understanding of several structural and mechanistic aspects of biological molecules. They played a particularly important role in metal binding proteins, where the electronic effects of transition metals have to be explicitly taken into account for the correct representation of the underlying biochemical process. In this review, after a brief description of the basic concepts of the QM/MM method, we provide an overview of its capabilities using selected examples taken from our work. Specifically, we will focus on heme peroxidases, metallo-β-lactamases, α-synuclein and ligase ribozymes to show how this approach is capable of describing the catalytic and/or structural role played by transition (Fe, Zn or Cu) and main group (Mg) metals. Applications will reveal how metal ions influence the formation and reduction of high redox intermediates in catalytic cycles and enhance drug metabolism, amyloidogenic aggregate formation and nucleic acid synthesis. In turn, it will become manifest that the protein frame directs and modulates the properties and reactivity of the metal ions.

The dynamics and energetics related to the release of chemisorbed hydrogen from small-diameter single-walled carbon nanotubes is investigated by first-principles molecular dynamics simulations. Our results suggest a possible route for thermally-activated desorption of hydrogen from the nanotube sidewall, leading to formation of molecular H 2 , and shed light on the basic mechanisms of the reversible storage of hydrogen in carbon nanotubes. In agreement with recent experiments, simulations indicate carbon nanotubes as suitable materials for the reversible storage of hydrogen. Moreover, calculations point to the restoration of the π bond patterning of the sidewall as the driving force for the desorption of hydrogen from carbon nanotubes. [ABSTRACT FROM AUTHOR]

The success of mechanochemistry is continued with the targeted organic synthesis of functional nano-scale devices. In the present theoretical study, first principles molecular dynamics simulations are performed for a recently synthesized three-ring system that functions as a molecular reaction cascade. Mechanochemical and photochemical reaction conditions are investigated. The system was designed in a way that three bonds would break consecutively in mechanochemical and sonochemical setups. We succeeded to simulate the reaction mechanisms with first-principles molecular dynamics simulations and discuss the stereochemistry. [ABSTRACT FROM AUTHOR]

It is shown on the basis of the data of three complementary methods (NMR-relaxation, Car-Parrinello molecular dynamics and quantum-chemical calculations) that the environment of the cation Ca 2 + in aqueous solutions consists of two layers with different molecular mobility: the number of water molecules in the first hydration shell is n 1 = 6, and for the second hydration shell n 2 = 12. The obtained n 1 and n 2 values were slightly rounded up to the nearest integer values to make the model more clear-cut (it is significant that the required changes were considerably < 5%). [ABSTRACT FROM AUTHOR]

Eight ethanolamine-core-like stabilizers of zinc acetate dihydrate (ZAD) are compared by means of density functional theory simulations (Gaussian optimizations and Car-Parrinello molecular dynamics). HOMO and LUMO are described and located, suggesting that photodegradation implies Zn reduction. Substituent effects on the thermal and optical degradation of the precursor formed by the aminoalcohols with ZAD are described. The Zn-ligand systems are analyzed in detail, and molecular dynamics allows to establish the classification of the aminoalcohols according to the stability of the ZnN bond. Unless the amount of nitrogen is well controlled, nitrogen-based additives should be avoided as ZAD stabilizers in the synthesis of pure ZnO. [ABSTRACT FROM AUTHOR]

Sulfur mustard (SM) is one of the most dangerous chemical compounds used against humans, mostly at war conditions but also in terrorist attacks. Even though the sulfur mustard has been synthesized over a hundred years ago, some of its molecular properties are not yet resolved. We investigate the structural flexibility of the SM molecule in the gas phase by Car–Parrinello molecular dynamics simulations. Thorough conformation analysis of 81 different SM configurations using density functional theory is performed to analyze the behavior of the system at finite temperature. The conformational diversity is analyzed with respect to the formation of intramolecular blue-shifting C H⋯S and C H⋯Cl hydrogen bonds. Molecular dynamics simulations indicate that all structural rearrangements between SM local minima are realized either in direct or non-direct way, including the intermediate structure in the last case. We study the lifetime of the SM conformers and perform the population analysis. Additionally, we provide the anharmonic dynamical finite temperature IR spectrum from the Fourier Transform of the dipole moment autocorrelation function to mimic the missing experimental IR spectrum. [ABSTRACT FROM AUTHOR]

We present Car–Parrinello molecular dynamics simulations—combined with metadynamics—of the reactions accompanying the capture of CO 2 in an aqueous amine solution. The selected amine is 2-amino-2-methyl-1,3-propanediol, which has been investigated experimentally in the search for optimum absorbents. In analogy with the empirical search, we use as reference aqueous monoethanolamine (MEA) at 30 wt%, namely the chemical absorbent most frequently used for the removal of CO 2 from combustion gases. In particular, we refer to our own results which have led to a detailed characterization of several reaction paths for the absorption of CO 2 and the amine regeneration (Ma et al. in J Chem Theory Comput 11:3189, 2015). Our simulations refer to the zwitterion mechanism leading to the formation of a carbamate or carbamic acid and to the release of the molecule in solution. The scenario established for the reactions in MEA is confirmed, and in particular the role of the zwitterion mechanism also for CO 2 release. We find that the difference in the structure of the two molecules does not influence the dynamics of either the formation or the dissociation of the zwitterion. However, it affects its interaction with water in a significant way, thus reducing the probability of carbamate formation and its stability in solution. [ABSTRACT FROM AUTHOR]

With a long term objective of investigating the molecular interactions of vanadium ions with different moieties in the conventional vanadium redox flow battery (VRFB) aqueous electrolyte solution, as well as with the additives in the electrolyte, force-field parameters for vanadium ions are proposed. The parameterization of vanadium ions is performed on the basis of first solvation shell structure for vanadium ions in water obtained by density functional theory (DFT) calculations. Car-Parrinello molecular dynamics (CPMD) simulations were performed to benchmark the proposed force field parameters in the condensed phase environment. The water–vanadium interactions obtained by the proposed parameters are also compared with the extended X-ray absorption fine structure (EXAFS) data in the literature. (Krakowiak et al., Inorganic Chemistry. 51, 2012, 9598–9609.) The regular octahedral structure of oxygen atoms around V 2 + and V 3 + and distorted octahedral structure of oxygen atoms around V 4 + and V 5 + , as revealed by EXAFS, are reproduced accurately by the suggested force-field parameters. These validated parameters can now be used to perform molecular dynamics simulations on the VRFB electrolyte solution to obtain fundamental understanding of the effect of different additives on solubility and thermal stability of vanadium ions within the VRFB electrolyte. [ABSTRACT FROM AUTHOR]