Researcher: Yurtsever, İsmail Ersin
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Yurtsever, İsmail Ersin
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Publication Metadata only A mixed basis with off-center Gaussian functions for the calculation of the potential energy surfaces for pi-stacking interactions: dimers of benzene and planar C-6(Springer, 2015) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129A practical mixed basis set was developed to facilitate accurate calculations of potential energy surfaces for pi-stacking interactions. Correlation consistent basis sets (cc-PVXZ) were augmented by p-type Gaussian functions placed above and below the planes of C-6 moieties. Moller-Plesset (MP2, SCS-MP2) and coupled cluster [CCSD(T)] calculations show that such generated basis sets provide an accurate description of p-stacking systems with favorable computation times compared to the standard augmented basis sets. The addition of these off-center functions eliminates the linear dependence of the augmented basis sets, which is one of the most encountered numerical problems during calculation of the oligomers of polyaromatic hydrocarbons (PAH). In this work, we present a comparative study of the general characteristics of the potential energy surfaces for the parallel stacked and T-shape conformations of benzene and planar C6 clusters, using a combination of cc-PVXZ and our optimized functions. We discuss properties, such as the depth and curvature of the potential functions, short and long distance behavior, and the frictional forces between two model monomers.Publication Metadata only Chaos in rotating triatomic clusters(Editions Physique, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Lyapunov exponent distributions of rotating triatomic Lennard-Jones clusters are calculated to analyze the effects of the vibrational and rotational motion on the extent of chaotic behavior. Initial momentum components are assigned to atoms either to rotate the clusters around symmetry axes or to generate random angular momenta. In both cases, it is seen that the initial kinetic energy assigned to vibrational modes is the dominant factor which determines the degree of chaos.Publication Metadata only A coarse graining approach in molecular simulations: fuzzy potentials(Istanbul Technical University, 2003) Department of Chemistry; Department of Chemistry; Yurtsever, İsmail Ersin; Eşsiz, Şebnem; Faculty Member; Undergraduated Student; Department of Chemistry; College of Sciences; College of Sciences; 7129; 191615A new representation for interaction potential functions is presented. Unlike the orthodox approaches, the potential function is not a fixed function in terms of internuclear coordinates but a probabilistic one which contains information over a wide range of angular degrees of freedom. It is shown that such approaches can provide practical solutions for bulk systems of high density.Publication Metadata only Pi-stack dimers of small polyaromatic hydrocarbons: a path to the packing of graphenes(Amer Chemical Soc, 2009) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129MP2 calculations of the stacking energy are reported for the dimers of a set of polycyclic aromatic hydrocarbons. The interaction strengths and their dependence on the shape-dependent measures as well as the aromatic character of the monomer are studied. For small systems involving four to six rings, the noncovalent interactions seem to be independent of the shape of the monomers. The most preferred conformations for parallel stacked dimers are not aligned exactly but off-center with small shifts; however, these shifts are on the order of 1 angstrom, and the energy necessary to keep them aligned is less than 0.5 kcal/mol per ring. Small-angle rotations within the molecular planes also do not require much energy, and in some cases they lead to stronger interactions.Publication Metadata only Quenching vibrations of cesium dimers by He at low and ultralow temperatures: quantum dynamical calculations(Springer, 2011) Caruso, D.; Tacconi, M.; Bovino, S.; Gianturco, F. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129This paper analyses in detail the energy redistribution from the upper vibrational levels of Cs dimers, thought to be obtained from initial recombination processes that generate excited internal states of the triplet configuration (3) I pound (u) (+) . Their quenching is examined as they are made to further collide with (4)He buffer gas at temperatures below and around 100 mK. The relevant cross sections are computed by using a multichannel quantum dynamical approach and employ a full, ab initio potential energy surface. Due to their smallness (see Ref. [R.B. Ross, J.M. Powers, T. Atashroo, W.C. Ermler, I.A. LaJohn, P. Christiansen, J. Chem. Phys. 93, 6654 (1999)]) the fine structure effects have not been explicitly included in this study. The final, cumulative cross-sections are discussed and analyzed in terms of the overall quenching behavior shown by different initial states of the dimer and in terms of the changing ratios between collisional cooling and vibrational quenching cross sections as a function of trap temperature. The corresponding quenching rates are also computed and analysed.Publication Metadata only Influence of competitive hydrogen bonding between hard and soft segments on the properties of siloxane and polyether-based segmented copolymers.(Amer Chemical Soc, 1999) Department of Chemistry; Department of Chemistry; N/A; Yılgör, İskender; Burgaz, Engin; Metin, Burak; Yurtsever, İsmail Ersin; Yılgör, Emel; Faculty Member; Undergraduate Student; Undergraduate Student; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of Sciences; N/A; 24181; 17956; N/A; N/A; 40527N/APublication Metadata only Theoretical study of vibrational spectroscopy of segmented poly(etherurethanes)(Amer Chemical Soc, 2000) N/A; Department of Chemistry; Department of Chemistry; Gördeslioğlu, Mehmet; Yılgör, Emel; Yurtsever, İsmail Ersin; Undergraduate Student; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 7129N/APublication Metadata only Reduction of viscosity of alumina nanopowder aqueous suspensions by the addition of polyalcohols and saccharides(Wiley, 2010) Akinc, Mufit; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Yar, Yasemin; Acar, Havva Funda Yağcı; Yurtsever, İsmail Ersin; PhD Student; Faculty Member; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 178902; 7129Flow behavior of nanosize alumina suspensions in the presence of polyalcohols was investigated. Viscosity of high solids content (35 vol%) alumina nanopowders was measured at room temperature. It was shown that after the first advancing shear rate branch, viscosity measurements show excellent reproducibility. All the suspensions showed the formation of large clusters, which are broken down as shear rate increases indicating reversible cluster breaking and reforming. Viscosity of suspensions decreases dramatically with up to 10 wt% polyalcohol addition. Only ethylene glycol showed an increase in viscosity indicating no interaction with the particle surface. The addition of polyalcohols is believed to prevent the formation of large and/or strong clusters by modifying the alumina particle surface. The exact nature and quantitative description of viscosity reduction by polyalcohol addition have yet to be established.Publication Metadata only Lyapunov instability in rotating systems from ergodic molecular dynamics simulations(Elsevier Science Bv, 2000) Calvo, Florent; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We improve the classical molecular dynamics (MD) method by a J-walking microcanonical Monte Carlo (MC) scheme to overcome broken ergodicity. This MC method rigorously samples the MD ensemble at finite energy and angular momentum. It is illustrated on the nonlinear dynamics of a 13-atom Lennard-Jones cluster.Publication Metadata only Structuring a quantum solvent around a weakly bound dopant: the He-Cs2((3)sigma u) complex(2009) Prosmiti, Rita; Delgado-Barrio, Gerardo; Villarreal, Pablo; Coccia, Emanuele; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The structure and energetics of 3,4HeCs2(3Σu) molecules are analyzed from first principles. Fixing the cesium dimer at its equilibrium distance, the electronic structure was determined through ab initio methods at the CCSD(T) level of theory using a large basis set to compute the interaction energies. At the T-shaped geometry, there is a shallow well with a depth of ∼2 cm−1 placed at R ∼6.75 Å, R being the distance from the center of mass of Cs2 to He. That depth gradually decreases to ∼0.75 cm−1, while R increases to about 11.5 Å at linear arrangements. A simple model of adding atom−atom Lennard-Jones potentials with well-depth and equilibrium distance parameters depending on the angular orientation was found to accurately reproduce the ab initio points. Using this analytical form, variational calculations at zero total angular momentum are performed, predicting a single bound level at ∼−0.106 (∼−0.042) cm−1 for the boson (fermion) species. Further calculations using Quantum Monte Carlo methods are carried out and found to be in good agreement with the variational ones. On the basis of the present results, such analytical expression could in turn be used to describe the structure and binding of larger complexes and therefore opens the possibility to further studies involving such aggregates.