Ajay Chaudhari

Many-body interaction in glycine–(water)3 complex using density functional theory method

Various configurations were investigated to find the most stable structures of glycine-(water)3 complex. Five different optimized conformers of glycine-(water)3 complex are obtained from density functional theory calculations using 6-311++G* basis set. Relaxation energy and many body interaction energies (two, three, and four body) are also calculated for these conformers. Out of the five conformers, the most stable conformer has the BSSE corrected total energy -513.917 967 7 Hartree and binding energy -27.28 Kcal/mol. It has been found that the relaxation energies, two body energies and three body energies have significant contribution to the total binding energy whereas four body energies are very small. The chemical hardness and chemical potential also confirmed the stability of the conformer having lowest total energy.

A computational study of microsolvation effect on ethylene glycol by density functional method

This study focuses on the conformational analysis of ethylene glycol-(water)n (n=1-3) complex by using density functional theory method and the basis set 6-311++G*. Different conformers are reported and the basis set superposition error corrected total energy is -306.767 5171, -383.221 3135, and -459.694 1528 for lowest energy conformer with 1, 2, and 3 water molecules, respectively, with corresponding binding energy -7.75, -15.43, and -36.28 kcal/mol. On applying many-body analysis it has been found that relaxation energy, two-body, three-body energy have significant contribution to the binding energy for ethylene glycol-(water)3 complex whereas four-body energies are negligible. The most stable conformers of ethylene glycol-(water)n complex are the cyclic structures in which water molecules bridge between the two hydroxyl group of ethylene glycol.

Hydrogen uptake capacity of C2H4Sc and its ions: A density functional study

We report the gravimetric hydrogen uptake capacity of C2H4Sc complex and isoelectronic ions using Density Functional Theory. We predict that C2H4Sc+ can bind maximum seven hydrogen molecules in dihydrogen form giving gravimetric uptake capacity of 16.2 wt %, larger by about 2 and 4 wt % than the neutral and anion, respectively. We also found that the interaction of hydrogen molecules with C2H4Sc+ ion is characteristically different than that with neutral and anion. Vibrational spectroscopic study reveals that C2H4Sc and isoelectronic ions are quantum mechanically stable with their characteristic change in respective identified mode. The large gravimetric H2 uptake capacity of C2H4Sc+ is well above the target specified by Department of Energy (DOE) by 2015.

Effect of surface roughness on diffusion limited reactions, a multifractal scaling analysis

Eley-Rideal diffusion limited reactions (DLR) were performed over different rough surfaces generated by Rain model. Multifractal scaling analysis has been carried out on the reaction probability distribution to investigate the effect of surface roughness on the chemical reactions. The results are compared with the DLRs over surface of diffusion limited aggregation (DLA).

Multifractal scaling analysis of autopoisoning reactions over a rough surface

Decay type diffusion-limited reactions (DLR) over a rough surface generated by a random deposition model were performed. To study the effect of the decay profile on the reaction probability distribution (RPD), multifractal scaling analysis has been carried out. The dynamics of these autopoisoning reactions are controlled by the two parameters in the decay function, namely, the initial sticking probability (Pini) of every site and the decay rate (m). The smaller the decay rate, the narrower is the range of α values in the α–f(α) multifractal spectrum. The results are compared with the earlier work of DLR over a surface of diffusion-limited aggregation (DLA). We also considered here the autopoisoning reactions over a smooth surface for comparing our results, which show clearly how the roughness affects the chemical reactions. The q–τ(q) multifractal curves for the smooth surface are linear whereas those for the rough surface are nonlinear. The range of α values in the case of a rough surface is wider than that of the smooth surface.

Can ionization induce an enhancement of hydrogen storage in Ti2–C2H4 complexes?

We predicted here gravimetric hydrogen storage capacity of Ti2–C2H4 and Ti2–C2H4+ complexes using density functional theory (DFT) method. The number of adsorbed H2 on Ti2–C2H4 is limited to ten. It has been seen that controlling the charge-state of this complex enhances its gravimetric hydrogen uptake and the metal bond strength. The resulting cationized complex then adsorbs two additional H2 molecules than the neutral complex. In addition, we elucidated the effect of exchange and correlation functionals in DFT on H2 adsorption energy of these complexes. Molecular dynamics simulations were also carried out to confirm whether the complex adsorbs H2 molecules at a finite temperature. The H2 uptake capacity of a complex from simulations is the same as that from the geometry optimization only if the H2 adsorption was energetically favourable i.e. with the positive Gibbs free corrected H2 adsorption energy.

Improved H2 uptake capacity of transition metal doped benzene by boron substitution

The effect of boron substitution on hydrogen storage capacity of transition metal (TM) doped benzene is studied using density functional theory and the second order Moller–Plesset method with aug-cc-pVDZ basis set. Out of the six carbon atoms in a benzene ring, two are substituted by boron atoms. The structures considered here are C4B2H6TM (TM = Sc, Ti, V). Four, four and three H2 molecules can be adsorbed on unsubstituted C6H6Sc, C6H6Ti and C6H6V complexes, respectively, whereas upon boron substitution one additional H2 molecule gets adsorbed on each of these complexes. The H2 uptake capacity of C4B2H6Sc, C4B2H6Ti and C4B2H6V obtained is 7.71, 7.54 and 5.99 wt%, respectively. Gibbs free energy corrected adsorption energies show that H2 adsorption on C4B2H6Sc is energetically unfavorable whereas it is favorable on C4B2H6Ti and C4B2H6V at ambient conditions. Various interaction energies for the H2 adsorbed complexes are obtained using a many-body analysis technique. The H2 desorption temperature for boron substituted TM doped benzene is lower than that for TM doped benzene for all the three systems. Molecular dynamics simulations show that loosely bonded H2 molecules in C4B2H6Sc(5H2) and C4B2H6Ti(5H2) complexes fly away during the simulation, thereby showing lower H2 uptake capacity of these complexes than that obtained by electronic structure calculations.

Closoborate-transition metal complexes for hydrogen storage

We report hydrogen uptake capacity of early transition metal (TM) atom (Sc, Ti and V) decorated closoborate (B6H6) using density functional theory and second order Moller–Plesset method. Maximum of four hydrogen molecules can be adsorbed on B6H6Sc, B6H6Ti and B6H6V complex with their gravimetric hydrogen uptake of 6.51, 6.36, 6.21 wt% respectively. We have used M06, B3LYP and MP2 methods with 6-311++G** basis set for the study. The Gibbs free energy corrected adsorption energies show that adsorption of four H2 molecules on B6H6Ti and B6H6V is energetically favorable whereas it is unfavorable on B6H6Sc at 298.15 K at M06/6-311++G** and B3LYP/6-311++G** level. Many-body analysis approach has been used here to study the nature of interaction between adsorbed H2 molecules and the substrate and that between hydrogen molecules in a complex. The binding energy of B6H6Sc(4H2), B6H6Ti(4H2) and B6H6V(4H2) complex is found to be 39.44, 58.43 and 51.03 kcal mol−1 respectively using M06/6-311++G** level of theory. Interaction between inorganic material-metal complexes with adsorbed H2 molecules is found to be attractive for all the three complexes. The charge transfer between Ti and adsorbed H2 molecules is more than that for Sc and V. The HOMO–LUMO gap shows that all the three H2 adsorbed complexes are kinetically stable. The dimers of TM-closoborate complexes in head-to-tail type configuration and multi-transition metal atom decorated closoborate complexes have also been studied. In both the cases number of H2 molecules adsorbed per TM atom is not affected neither by dimerization nor multi-transition metal atom decoration.

Dynamic scaling of diffusion-limited reactions over fractal surfaces: computer simulation

Computer simulations are performed to examine the effect of geometrical heterogeneity on chemical reaction occurring over a fractal surface of diffusion-limited aggregation (DLA). Eley–Rideal diffusion-limited reaction (DLA) is chosen as our model reaction system. Dynamic scaling theory, developed for surface growth model, is applied in this work on chemical reaction model revealing two order parameters, a and b, in different time domains, i.e. a ¼� 0:74, b ¼� 0:48 for perfect sticking cases, and a ¼� 0:72, b ¼� 0:5 for cases of lower sticking probability. Surfaces of different fractal dimensions are also considered, where the values of b in both cases and a values in the perfect sticking case do not change obviously. In the cases of lower sticking probability, a values are decreased when fractal dimension approaches to 2. Comparisons are made to the surface roughening model where both order parameters are positive. # 2002 Elsevier Science B.V. All rights reserved.

Eley–Rideal diffusion limited reactions over rough surface

The effect of surface roughness on Eley–Rideal diffusion limited reactions is studied. The rough surfaces are generated using a random deposition model and a random deposition with diffusion model. The former model generates the rough surface with no correlations between the heights of different columns whereas the latter generates the rough surface with correlations between the heights of different columns. Multifractal scaling analysis has been carried out on the reaction probability distribution. The reaction probability distribution has a wider range for the surface of random deposition than that of random deposition with diffusion.