External double reference method to study concentration and temperature dependences of chemical shifts determined on a unified scale. Dynamics and metastable surface structure of double atomic layer of water molecules and ions at the interface between KBr c and water. Riegel, F. Terrau, A. Eisenberg, C. Petzhold and D. Dynamics and structure of an amphiphilic triblock copolymer of styrene and 5- N,N-diethylamino isoprene in selective solvents. Besnard, T.
Tassaing and Y. Local density inhomogeneities detected by Raman scattering in supercritical hexafluorobenzene. Musso, F. Matthai, D. Keutel and K. Raman noncoincidence effect: A spectroscopic manifestation of the intermolecular vibrational coupling in dipolar molecular liquids. Spectroscopy of interparticle interactions in ionic and molecular liquids: Novel approaches.
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Peripheral substituent and solvent effects on the aggregation and photochemical properties of copper II phthalocyanine and copper II phthalocyanine-3,4',4'',4'''-tetrasulfonic anion. Zoe Cournia, A.
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Vaiana, G. Ullmann and J. Structure of the porphyrazine monolayer at the air-water interface: Computer simulation. Translational and rotational dynamics in supercritical methanol from molecular dynamics simulation. Origin of the enhanced structural and reorientational relaxation rates in the presence of relatively weak dc electric fields.
Transport properties of diatomic ions in moderately dense gases in an electrostatic field. In Figure 4 the values obtained for the O - - H distances and the H - - O-H angles are in the intervals generally accepted to characterize hydrogen bonding: H - - O distance in the interval ca. The dimers structures in Figure 4 can be interpreted as a supermolecule with weak energy of torsion along the O-H - - - O segment. This rotation like effect contributes to increase the liquid entropy with low influence in the cohesion energy.
To further investigate the similarity between dimer interaction, pair energy distributions are shown in Figure 5. As the curves obtained with all QM-FF models are very similar, only two examples are shown. As discussed elsewhere, the bimodal shape of these curves is characteristic of hydrogen bonded liquids.
There is a remarkable agreement between the positions of features in Figure 6 with the ones in the O-O radial distribution presented on Figure 3. As shown in Table 1 there is remarkable agreement between the values of theta obtained for low energy dimers searched along the MMC trajectory. At distances greater than 3. Therefore, properties related to dipole moment correlations, such as the dielectric permittivity, DP, are expected to have dependences with the dihedral angle distribution. Densities and enthalpies of vaporization. Theoretical values obtained for density and enthalpy of vaporization of liquid ethanol at 1.
One observes in Table 1 a good agreement between theoretical results and experimental values. Therefore, the agreement between the theoretical results obtained for density and enthalpy of vaporization using different QM-FF methods is in contrast with the discrepancies found in the dihedral angle distributions, as shown in Figures 1 and 2.
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Apparently, the differences between gauche and trans populations obtained using different QM-FF methods are not a problem for obtaining density and enthalpy of vaporization in close agreement with experimental data. This finding is also in agreement with the dimer energies and geometry parameters shown if Figure 4 and also with the pair energy distributions presented in Figure 5.
Following usual procedures the total energy of the system is partitioned into force field and quantum mechanical contributions.
Classical contributions are calculable using standard force field and the main MMC program includes MOPAC 6 is as a sub-routine to perform quantum calculations using the facilities implemented in this program. The program was used to study liquid ethanol in the NpT ensemble at 1 atm and K.
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The results obtained for the dihedral angle distributions shows noticeable differences regarding the populations of trans and gauche conformers. These results are further discussed in the electronic supplementary information section of this article. Features observed in the Oxygen-Oxygen and Hydrogen-Oxygen radial distributions functions show strong influence of hydrogen bonded dimmers. These distributions are mainly unaffected by the differences in conformers population. Therefore, the hydrogen bond drives the dipole-dipole orientation to a different pattern when compared to the ones expected for non-hydrogen bonded dipolar molecules.
This behavior was also observed for other hydrogen bonded liquids. As a consequence, the values obtained for liquid density and enthalpy of vaporization are also in very good accord. As concluding remark, the possibility of using MOPAC to calculate the internal energy as well as other quantum mechanical information is a considerable improvement to study complex systems using computer simulations. Other applications are under progress. The author is grateful to his former students and collaborators for support and encouragement.
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Supplementary Information. Heermann, D.
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- Prof Amalendu Chandra,Dept of Chemistry, IIT Kanpur.
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Rappaport, D. Frenkel, D. Allen, T. Dykstra, C. Jorgensen, W. Vreven, T. Theory Comput. Tse, T. Aqvist, J. Warshel, A. Kapral, R. Bruice, T. Prado, C. Del; Youngs, T. Fileti, E. Kaminski, G. B , , Biswas, P. Tishchenko, O. Coolidge, M. Seiler Res. Metropolis, N. Onsager, L. Zwanzig, R. Schaftenaar, G.
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