arXiv subjects

Vitaly V. Chaban

Publications and source records attributed to Vitaly V. Chaban.

At least 37 records · Page 2Linked to original sources

arXiv2017

A Weakly Coordinating Anion Substantially Enhances Carbon Dioxide Fixation by Calcium and Barium Salts

Carbon dioxide fixation and storage constitute a drastically important problem for the humanity nowadays. We hereby publish a new solution based on the alkaline earth salts with a weakly coordinating anion, tetrakis(pentafluorophenyl)borate. The proposed solution was validated using a robust combination of global minimum search and molecular dynamics simulations utilizing a well-tested, reliable semiempirical Hamiltonian to monitor chemical reactions. Calcium tetrakis(pentafluorophenyl)borate captures 5.5 CO2 molecules per mole, whereas barium tetrakis(pentafluorophenyl)borate captures 3.6 CO2 molecules per mole. These capacities are much higher, as compared to the established carbonate technology, which fixes only one CO2 molecule per one metal atom. The conducted simulations reveal that electrostatic binding of CO2 to alkaline earth cations is more technologically interesting than formation of carbonate salts. Our simulation results can be directly validated by sorption measurements.

cond-mat.mtrl-sci↗

arXiv2017

Electronic and Thermodynamic Properties of the Amino- and Carboxamido-Functionalized C-60-Based Fullerenes: Towards Non-Volatile Carbon Dioxide Scavengers

Development of new greenhouse gas scavengers is actively pursued nowadays. Volatility caused solvent consumption and significant regeneration costs associated with the aqueous amine solutions motivate search for more technologically and economically advanced solutions. We hereby used hybrid density functional theory to characterize thermodynamics, structure, electronic and solvation properties of amino and carboxamido functionalized C60 fullerene. C60 is non-volatile and supports a large density of amino groups on its surface. Attachment of polar groups to fullerene C60 adjusts its dipole moment and band gap quite substantially, ultimately resulting in systematically better hydration thermodynamics. Reaction of polyaminofullerenes with CO2 is favored enthalpically, but prohibited entropically at standard conditions. Free energy of the CO2 capture by polyaminofullerenes is non-sensitive to the number of amino groups per fullerene. This result fosters consideration of polyaminofullerenes for CO2 fixation.

cond-mat.mtrl-sci↗

arXiv2017

Structure, Thermodynamic and Electronic Properties of Carbon-Nitrogen Cubanes and Protonated Polynitrogen Cations

Energy generation and storage are at the center of modern civilization. Energetic materials constitute quite a large class of compounds with a high amount of stored chemical energy that can be released. We hereby use a combination of quantum chemistry methods to investigate feasibility and properties of carbon-nitrogen cubanes and multi-charged polynitrogen cations in the context of their synthesis and application as unprecedented energetic materials. We show that the stored energy increases gradually with the nitrogen content increase. Nitrogen-poor cubanes retain their stabilities in vacuum, even at elevated temperatures. Such molecules will be probably synthesized at some point. In turn, polynitrogen cations are highly unstable, except N8H+, despite they are isoelectronic to all-carbon cubane. Kinetic stability of the cation decays drastically as its total charge increases. High-level thermodynamic calculations revealed that large amounts of energy are liberated upon decompositions of polynitrogen cations, which produce molecular nitrogen, acetylene, and protons. The present results bring a substantial insights to the design of novel high energy compounds.

cond-mat.mtrl-sci↗

arXiv2017

Imidazolium Ionic Liquid Mediates Black Phosphorus Exfoliation while Preventing Phosphorene Decomposition

Forthcoming applications in electronics and optoelectronics make phosphorene a subject of vigorous research efforts. Solvent-assisted exfoliation of phosphorene promises affordable delivery in industrial quantities for future applications. We demonstrate, using equilibrium, steered and umbrella sampling molecular dynamics, that the 1-ethyl-3- methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquid is an excellent solvent for phosphorene exfoliation. The presence of both hydrophobic and hydrophilic moieties, as well as substantial shear viscosity, allows [EMIM][BF4] simultaneously to facilitate separation of phosphorene sheets and to protect them from getting in direct contact with moisture and oxygen. The exfoliation thermodynamics is moderately unfavorable, indicating that an external stimulus is necessary. Unexpectedly, [EMIM][BF4] does not coordinates phosphorene by p-electron stacking with the imidazole ring. Instead, the solvation proceeds via hydrophobic side chains, while polar imidazole rings form an electrostatically stabilized protective layer. The simulations suggest that further efforts in solvent engineering for phosphorene exfoliation should concentrate on use of weakly coordinating ions and grafting groups that promote stronger dispersion interactions, and on elongation of nonpolar chains.

cond-mat.mtrl-sci↗

arXiv2016

Isomerism in Quantum Dots: Geometries, Band Gaps, Dipole Moments, Ionization Energies and Heats of Formation

Quantum dots (QDs) are applied in a variety of fields ranging from photovoltaics to biomedical imaging. Even the smallest QDs present a complicated potential energy surface characterized by a large set of stationary points. Each local minimum is an isomer of QD of given composition. An established theoretical methodology is hereby employed to obtain geometries of the QD isomers (Cd16Se16, Cd16Se16, Zn16S16, Zn16Se16) and predict their fundamental electronic and thermodynamic properties. Significantly scattered heats of formation, with an amplitude up to 1304 kcal mol-1 in Cd16S16, were found for the most and the least thermodynamically stable isomers of QDs. The most shallow transition points can unlikely be observed in the experiments at finite temperature, since they are able to transform into more stable isomers upon thermal motion. Dipole moment is the most sensitive property to the QD isomer geometry. A global energy search technique was demonstrated to be an efficient tool to systematically identify isomers of QDs.

cond-mat.mtrl-sci↗

arXiv2015

Acetone as a Polar Cosolvent for Pyridinium-Based Ionic Liquids

The work reports transport and structure properties of the three pyridinium-based ionic liquids (RTILs) - N-butylpyridinium hexafluorophosphate [BPY][PF6], N-butylpyridinium trifluorosulfonate [BPY][TF] and N-butylpyridinium bis(trifluoromethanesulfonyl)imide [BPY][TFSI] - in their mixtures with acetone (ACET). The ionic conductivity maximum occurs at 10 mol% RTIL, irrespective of the anion. The absolute ionic conductivity value of [BPY][TF] is higher than those of other RTILs. This is explained by a weaker cation-anion binding than that in [BPY][PF6] and smaller anion size than that of [BPY][TFSI]. All the investigated RTILs are infinitely miscible with ACET, which boosts their diffusivity and conductivity. A small viscosity of ACET favors a drastic viscosity decay in the RTIL-ACET mixtures. Structure analysis (radial distribution functions, ionic clusters) of the mixtures are in line with their transport properties providing a reliable microscopic interpretation of the observed macroscopic properties. As a molecular co-solvent, ACET constitutes an interesting alternative and competitor to more intensively investigated liquids.

cond-mat.soft↗

arXiv2015

Solvation of the Morpholinium Cation in Acetonitrile. Effect of an Anion

Ionic liquids constitute a fast growing class of compounds finding multiple applications in science and technology. Morpholinium-based ionic liquids (MBILs) and their mixtures with polar molecular co-solvents are interesting as sustainable electrolyte systems for electrochemistry. We investigate local structures of protic and propton-free morpholinium cations in acetonitrile (ACN) using semi-empirical molecular dynamics (MD) simulations. An impact of an anion (acetate) on the cation solvation regularities is discussed. Unlike oxygen, nitrogen of the morpholine ring is a strong electrophilic binding center. This site is responsible for the interactions of the cation with the solvent and with the anion. In protic MBILs, the role of nitrogen is delegated to the proton, which is linked to nitrogen. The acetate anion weakens solvation of the cation due to occupation of space near nitrogen or proton. The analysis reveals a favorable solvation of MBILs in ACN, which is a prerequisite for a new high-performance electrolyte system. The reported structural data are validated through a point-to-point comparison with the MP2 post-Hartree-Fock theory.

cond-mat.mtrl-sci↗

arXiv2015

Polypeptide A9K at Nanoscale Carbon: Simulation Study

An amphiphilic nature of the surfactant-like peptides is responsible for their propensity to aggregate at the nanoscale. These peptides can be readily used for a non-covalent functionalization of nanoparticles and macromolecules. This work reports an observation of supramolecular ensembles consisting of ultrashort carbon nanotubes (USCNTs), graphene (GR) and A9K polypeptide formed by lysine and arginine. Potential of mean force (PMF) is used as a major descriptor of the CNT-A9K and GR-A9K binding process, supplementing structural data. The phase space sampling is performed by multiple equilibrium molecular dynamics simulations with position restraints, where applicable. Binding in all cases was found to be thermodynamically favorable. Encapsulation in the (10,10) USCNT is particularly favorable. Curvature of external surface does not favor binding. Thus, binding of A9K at GR is stronger than its binding at the outer sidewall of USCNTs. Overall, the presented results favor non-covalent functionalization of nanoscale carbons that are considered interesting in the fields of biomaterials, biosensors, biomedical devices, and drug delivery.

cond-mat.mtrl-sci↗

arXiv2015

Structure and Energetics of Graphene Oxide Isomers: Ab Initio Thermodynamic Analysis

Graphene oxide (GO) holds significant promise for electronic devices and nanocomposite materials. A number of models were proposed for GO structure, combining carboxyl, hydroxyl, carbonyl and epoxide groups at different locations. The complexity and variety of GO isomers, whose thermodynamic stability and formation kinetics depend on applied conditions, make determination of GO structure with atomistic precision challenging. We report high level theoretical investigation of multiple molecular configurations, which are anticipated in GO. We conclude that all oxygen containing groups at the GO surface are thermodynamically permitted, whereas the edge positions are systematically more favorable than the center and side positions. We discuss a potentially novel type of chemical bond or bonding reinforcement in GO, which consists of a covalent bond and a strong electrostatic contribution from a polarized graphene plane. We observe and analyze significant modifications of graphene geometry and electronic structure upon oxidation. The reported thermodynamic data guide experiments aimed at deciphering GO chemical composition and structure, and form the basis for predicting GO properties required for nano-technological applications.

cond-mat.mtrl-sci↗

arXiv2015

Are Fluorination and Chlorination of the Morpholinium-Based Ionic Liquids Favorable?

Room-temperature ionic liquids (RTILs) constitute a fine-tunable class of compounds. Morpholinium-based cations are new to the field. They are promising candidates for electrochemistry, micellization and catalytic applications. We investigate halogenation (fluorination and chlorination) of the N-ethyl-N-methylmorpholinium cation from thermodynamics perspective. We find that substitutional fluorination is much more energetically favorable than substitutional chlorination, although the latter is also a permitted process. Although all halogenation at different locations are possible, they are not equally favorable. Furthermore, the trends are not identical in the case of fluorination and chlorination. We link the thermodynamic observables to electron density distribution within the investigated cation. The reported insights are based on the coupled-cluster technique, which is a highly accurate and reliable electron-correlation method. Novel derivatives of the morpholinium-based RTILs are discussed, motivating further efforts in synthetic chemistry.

cond-mat.mtrl-sci↗

arXiv2015

Enhanced Stability of the Model Mini-protein in Amino Acid Ionic Liquids and Their Aqueous Solutions

Using molecular dynamics simulations, the structure of model mini-protein was thoroughly characterized in the imidazolium-based amino acid ionic liquids and their aqueous solutions. We report that the mini-protein is more stable when AAIL is added as a cosolvent. Complete substitution of water by organic cations and anions further results in hindered conformational flexibility of the mini-protein. This observation suggests that AAILs are able to defend proteins from thermally induced denaturation. We show by means of radial distributions that the mini-protein is efficiently solvated by both solvents due to agood mutual miscibility. However, amino acid based anions prevail in the first coordination sphere of the mini-protein.

physics.bio-ph↗

arXiv2015

Halogenation of Imidazolium Ionic Liquids. Thermodynamics Perspective

Imidazolium cations are promising for anion exchange membranes, and electrochemical applications and gas capture. They can be chemically modified in many ways including halogenation. Halogenation possibilities of the imidazole ring constitute a particular interest. This work investigates fluorination and chlorination reactions of all symmetrically non-equivalent sites of the imidazolium cation. Halogenation of all carbon atoms is thermodynamically permitted. Out of these, the most favorable site is the first methylene group of the alkyl chain. In turn, the least favorable site is carbon of the imidazole ring. Temperature dependence of enthalpy, entropy, and Gibbs free energy at 1 bar is discussed. The reported results provide an important guidance in functionalization of ionic liquids in search of task-specific compounds.

cond-mat.mtrl-sci↗

arXiv2015

Ionization of Cucurbiturils as a Pathway to More Stable Host-Guest Complexes

Cucurbiturils are particularly interesting to chemists, because these macrocyclic molecules are suitable hosts for an array of neutral and cationic species. It is believed that the host-guest binding originated from hydrophobic interactions and ion-dipole interactions in the case of cationic guests. The fact that an elementary unit of cucurbiturils consists of two fused imidazole rings, which ionize readily, has remained largely unnoticed up to now. This work reports ionized cucurbiturils and their binding to C60 fullerene using versatile electronic-precision description. The methodology is based on density functional theory. We assert that cationization of cucurbiturils fosters C60-cucurbituril binding due to polarization of electron density in C60. Therefore, more stable host-guest complexes can be derived.

cond-mat.mtrl-sci↗

arXiv2015

Can Inorganic Salts Tune Electronic Properties of Graphene?

Electronic properties of graphene quantum dots (GQDs) constitute a subject of intense scientific interest. Being smaller than 20 nm, GQDs contain confined excitons in all dimensions simultaneously. GQDs feature a non-zero band gap and luminesce on excitation. Tuning their electronic structure is an attractive goal with a technological promise. In this work, we apply density functional theory to study an effect of neutral ionic clusters adsorbed on GQD surface. We conclude that both HOMO and LUMO of GQD are very sensitive to the presence of ions and to their distance from the GQD surface. However, the alteration of the band gap itself is modest, as opposed to the case of free ions (recent reports). Our work fosters progress in modulating electronic properties of nanoscale carbonaceous materials.

cond-mat.mtrl-sci↗

arXiv2015

Temperature Dependent Interaction Non-Additivity in the Inorganic Ionic Clusters

Interaction non-additivity in the chemical context means that binding of certain atom to a reference atom cannot be fully predicted from the interactions of these two atoms with other atoms. This constitutes one of key phenomena determining an identity of our world, which would have been much poorer otherwise. Ionic systems provide a good example of the interaction non-additivity in most cases due to electron transfer and delocalization effects. We report Born-Oppenheimer molecular dynamics (BOMD) simulations of LiCl, NaCl, and KCl at 300, 1500, and 2000 K. We show that our observations originate from interplay of thermal motion during BOMD and cation nature. In the case of alkali cations, ionic nature plays a more significant role than temperature. Our results bring fundamental understanding of electronic effects in the condensed phase of ionic systems and foster progress in physical chemistry and engineering.

physics.chem-ph↗

arXiv2015

Nitrogen-Nitrogen Bonds Violate Stability of N-Doped Graphene

Two-dimensional alloys of carbon and nitrogen represent an urgent interest due to prospective applications in nanomechanical and optoelectronic devices. Stability of these chemical structures must be understood as a function of their composition. The present study employs hybrid density functional theory and reactive molecular dynamics simulations to get insights regarding how many nitrogen atoms can be incorporated into the graphene sheet without destroying it. We conclude that (1) C:N=56:28 structure and all nitrogen-poorer structures maintain stability at 1000 K; (2) stability suffers from N-N bonds; (3) distribution of electron density heavily depends on the structural pattern in the N-doped graphene. Our calculations support experimental efforts on the production of highly N-doped graphene and tuning mechanical and optoelectronic properties of graphene.

cond-mat.mtrl-sci↗

arXiv2015

Strong Electronic Polarization of the C60 Fullerene by the Imidazolium-Based Ionic Liquids: Accurate Insights from Born-Oppenheimer Molecular Dynamics Simulations

Fullerenes are known to be polarizable due to the strained carbon-carbon bonds and high surface curvature. Electronic polarization of fullerenes is of steady practical importance, since it leads to non-additive interactions and, therefore, to unexpected phenomena. For the first time, hybrid density functional theory (HDFT) powered Born-Oppenheimer molecular dynamics (BOMD) simulations have been conducted to observe electronic polarization and charge transfer phenomena in the C60 fullerene at finite temperature (350 K). The non-additive phenomena are fostered by the three selected imidazolium-based room-temperature ionic liquids (RTILs). We conclude that although charge transfer appears nearly negligible in these systems, an electronic polarization is indeed significant leading to a systematically positive effective electrostatic charge on the C60 fullerene: +0.14e in [EMIM][Cl], +0.21e in [EMIM][NO3], +0.17e in [EMIM][PF6]. These results are, to certain extent, unexpected providing an inspiration to consider novel C60/RTILs systems. HDFT BOMD provides a powerful tool to investigate electronic effects in RTIL and fullerene containing nuclear-electronic systems.

cond-mat.mtrl-sci↗

arXiv2015

The Force Field for Amino Acid Based Ionic Liquids: Polar Residues

Ionic liquids (ILs) constitute one of the most active fields of research nowadays. Many organic and inorganic molecules can be converted into ions via relatively simple procedures. These ions can be combined into ILs. Amino acid based ILs (AAILs) represent a specific interest due to solubilization of biological species, participation in enzymatic catalysis, and capturing toxic gases. We develop a new force field (FF) for the seven selected AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions with polar residues. The anions were obtained via deprotonation of carboxyl group. We account for peculiar interactions between the anion and the cation by fitting electrostatic potential for an ion pair, in contrast to isolated ions. The van der Waals interactions were transferred from the CHARMM36 FF with minor modifications, as suggested by hybrid density functional theory. Compatibility between our parameters and CHARMM36 parameters is preserved. The developed interaction model fosters computational investigation of ionic liquids.

cond-mat.mtrl-sci↗