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.
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 halogen
ation (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.
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 identi
ty 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.
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.
Electronic polarization and charge transfer effects play a crucial role in thermodynamic, structural and transport properties of room-temperature ionic liquids (RTILs). These non-additive interactions constitute a useful tool for tuning physical chem
ical behavior of RTILs. Polarization and charge transfer generally decay as temperature increases, although their presence should be expected over an entire condensed state temperature range. For the first time, we use three popular pyridinium-based RTILs to investigate temperature dependence of electronic polarization in RTILs. Atom-centered density matrix propagation molecular dynamics, supplemented by a weak coupling to an external bath, is used to simulate the temperature impact on system properties. We show that, quite surprisingly, non-additivity in the cation-anion interactions changes negligibly between 300 and 900 K, while the average dipole moment increases due to thermal fluctuations of geometries. Our results contribute to the fundamental understanding of electronic effects in the condensed phase of ionic systems and foster progress in physical chemistry and engineering.
