Hydrogen bonding and infrared spectra of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/water mixtures : a view from molecular dynamics simulations

[Image: see text] Simulations of ab initio molecular dynamics have been performed for mixtures of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid and water. Statistics of donors and acceptors of hydrogen bonds has revealed that with increasing water content, hydrogen bonds between EMIM cations and TFSI anions are replaced by bonds to water molecules. In the mixture of liquids, the total number of bonds (from EMIM cations or water molecules) formed by TFSI acceptors increases. IR spectra obtained from ab initio molecular dynamics trajectories are in good agreement with literature data for ionic liquid/water systems. Analysis of oscillations of individual C–H and O–H bonds has shown correlations between vibrational frequencies and hydrogen bonds formed by an EMIM cation or water molecule and has indicated that the changes in the IR spectrum result from the decreased number of water–water hydrogen bonds in the mixture. The tests of DFTB methodology with tailored parameterizations have yielded reasonably good description of the IR spectrum of bulk water, whereas available parameterizations have failed in satisfactory reproduction of the IR spectrum of EMIM-TFSI/water mixtures in the region above 3000 cm(–1)

NaFSI and NaTFSI solutions in ether solvents from monoglyme to poly(ethylene oxide) : a molecular dynamics study

[Image: see text] Classical molecular dynamics simulations have been performed for a series of electrolytes based on sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide salts and monoglyme, tetraglyme, and poly(ethylene oxide) as solvents. Structural properties have been assessed through the analysis of coordination numbers and binding patterns. Residence times for Na–O interactions have been used to investigate the stability of solvation shells. Diffusion coefficients of ions and electrical conductivity of the electrolytes have been estimated from molecular dynamics trajectories. Contributions to the total conductivity have been analyzed in order to investigate the role of ion–ion correlations. It has been found that the anion–cation interactions are more probable in the systems with NaTFSI salts. Accordingly, the degree of correlations between ion motions is larger in NaTFSI-based electrolytes

Explicit and hybrid solvent models for estimates of parameters relevant to the reduction potential of ethylene carbonate

Using ethylene carbonate as a sample solvent, we investigated two molecular parameters used to estimate the reduction potential of the solvent: electron affinity, and the energy of the lowest unoccupied molecular orbital (LUMO). The results showed that the values of these parameters are inconsistent for a single ethylene carbonate molecule in vacuum calculations and in the continuous effective solvent. We performed a series of calculations employing explicit or hybrid (explicit/continuous) solvent models for aggregates of solvent molecules or solvated salt ions. In the hybrid solvent model, values of the two estimates extrapolated to an infinite system size converged to one common value, whereas the difference of 1 eV was calculated in the purely explicit solvent. The values of the gap between the highest occupied molecular orbital (HOMO) and the LUMO obtained in the hybrid model were significantly larger than those resulting from the explicit solvent calculations. We related these differences to the differences in frontier orbitals and changes of electron density obtained in the two solvent models. In the hybrid solvent model, the location of the additional electron in the reduced system usually corresponds to the LUMO orbital of the oxidized system. The presence of salt ions in the solvent affects the extrapolated values of the electron affinity and LUMO energy

Avoiding pitfalls of a theoretical approach : the harmonic oscillator measure of aromaticity index from quantum chemistry calculations

The concept of the harmonic oscillator measure of aromaticity (HOMA) is based on comparing the geo-metrical parameters of a studied molecule with the param-eters for an ideal aromatic system derived from bond lengths of the reference molecules. Nowadays, HOMA is routinely computed combining the geometries from quantum chem-istry calculations with the experimentally based parameter-ization. Thus, obtained values of HOMA, however, are bound to suffer from inaccuracies of the theoretical methods and strongly depend on computational details. This could be avoided by obtaining both the input geometries and the parameters with the same theoretical method, but efficiency of the error compensation achieved in this way has not yet been probed. In our work, we have prepared a benchmark set of HOMA values for 25 cyclic hydrocarbons, based on the all core CCSD(T)/cc-pCVQ(T)Z geometries, and used it to investigate the impact of different choices of the exchange– correlation functionals and basis sets on HOMA, calculated against the experimentally based (HOMA EP) or the consis-tently calculated (HOMA CCP) parameters. We show that using HOMA EP leads to large and unsystematic errors, and strong sensitivity to the choice of XC functional, basis set, and the experimental data for the reference geometry. This sensitivity is largely, although not completely attenuated in the consistent approach. We recommend the most suitable functionals for calculating HOMA in both approaches (HOMA EP and HOMA CCP), and provide the HOMA parameters for 25 studied exchange–correlation functionals and two popular basis sets

Characteristics of occurrence and problems of exploitation of geothermal waters in the Tatra`s basins of Central Western Carpathians area

Wody geotermalne występujące w nieckach otaczających Tatry - podhalańskiej, skoruszyńskiej, popradzkiej i liptowskiej tworzą ciąg hydrauliczny. Warunki hydrogeologiczne umożliwiają odnawianie tych zasobów, a ich źródłem są wody pochodzenia meteorycznego. Obecnie eksploatowane są wody termalne o temperaturze do 86°C i wykorzystywane są one głównie w basenach termalnych oraz w celach ciepłowniczych. Pozyskiwanie wód geotermalnych wiąże się z problemami eksploatacji takimi jak korozja, wytrącanie się minerałów, emisja radonu, czy dostarczaniem do środowiska ładunku chemicznego, bakteriologicznego i cieplnego.Geothermal water present in the basins surrounding Tatry - Podhale, Skoruszyna, Poprad and Liptov create a hydraulic string . Hydrogeological conditions allow renewal of these resources, and are the source of water of meteoric origin. Currently they are operated thermal water temperatures up to 86°C and are used mainly in thermal pools and heating purposes. Obtaining geothermal water has problems of operation such as corrosion, precipitation of minerals, radon emissions, or delivering cargo to the environment of chemical and bacteriological heat