BITS Faculty Publications
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Item Principle of maximum hardness: an accurate ab initio study(ACS, 1993) Roy, Ram KinkarIn this paper we test the principle of maximum hardness through an accurate quantum chemical calculation. Computations include extensive correlation and relaxation effects for the calculation of ionization potential and electron affinity. The molecule water has been chosen as a primary test case.Item Stationary multideterminantal coupled-cluster response(APS, 1994-03-01) Roy, Ram KinkarWe discuss a stationary version of the coupled-cluster response theory using multideterminantal model space. This brings in all the attendant advantages of a stationary theory for quasidegenerate cases.Item Change of Hardness and Chemical Potential in Chemical Binding: A Quantitative Model(ACS, 1994) Roy, Ram KinkarIn this paper we relate the change of chemical hardness and potential with the binding energies as the chemical binding takes place. We use a simple model to demonstrate that the hardness change is not only related to the binding energy of the molecule being formed, but also to the binding energies of the corresponding molecular cations and anions. Similar expressions are also derived for chemical potential. We have shown that our analysis can explain the existing data. The separated limit values of hardness and chemical potential are also derived. Two demonstrative calculations on the molecules H2 and HF are presented. The future potential of this model is discussed.chemical potentialItem Correlation of Polarizability, Hardness, and Electronegativity: Polyatomic Molecules(ACS, 1994) Roy, Ram KinkarIn this paper, for the first time we have correlated the hardness (η), softness (s), and polarizability (P) with the electronegativity and the distortion (ΔR) of a single bond in a complex polyatomic system. The study also shows some interesting: trends as different types of bonds are distorted. We have suggested a new concept, "local bond hardness", in a complex polyatomic system. The molecules H2O, CH4, CH3Cl, and CH3F are chosen as primary test cases.Item Hardness as a function of polarizability in a reaction profile(Elsiever, 1995-02-10) Roy, Ram KinkarIn this article, for the first time, we have correlated chemical hardness with polarizability when a single bond in a complex polyatomic molecule is distorted. A predominantly linear relation has been observed between the cube root of polarizability and hardness when various types of bonds are distorted. The molecules CH3Cl, CH3F and CH4 are chosen as typical example systems.Item Chemical Potential and Hardness for Open Shell Radicals: Model for the Corresponding Anions(ACS, 1995) Roy, Ram KinkarIn this article, we have obtained theoretical values of chemical potential and hardness for open shell free radicals using a wave function approach. The calculated values of the hardness are useful particularly for rank ordering of the corresponding anions. A ΔSCF procedure is used to obtain these values, and the results are compared with corresponding experimental values. The procedure also leads us to the reliability of the ΔSCF procedure for these quantities.Item The Local Hard−Soft Acid−Base Principle: A Critical Study(ACS, 1997) Roy, Ram KinkarThe recently proposed local hard−soft acid−base principle characterizes the reactive centers of two systems on the basis of equal Fukui functions or/and equal local softnesses. We make a quantum chemical study of this principle using ab initio and density functional calculations in cases where the global softnesses of the reacting systems are different. We consider reactions of a dimer cluster model of faujasite X-type zeolite with the probe molecules CO, NH3, and H2O.Item Change of Hardness and Chemical Potential in Chemical Binding: A Quantitative Model(ACS, 1994) Roy, Ram KinkarItem Local Softness and Hardness Based Reactivity Descriptors for Predicting Intra- and Intermolecular Reactivity Sequences: Carbonyl Compounds(ACS, 1998) Roy, Ram KinkarThe DFT-based reactivity descriptors “local softness” and “local hardness” are used as reactivity indices to predict the reactivity sequences (both intramolecular and intermolecular) of carbonyl compounds toward nucleophilic attack on them. The finite difference approximation is used to calculate local softness, whereas local hardness is approximated by −Vel/2N, where Vel is the electronic part of the molecular electrostatic potential. Both aldehydes and ketones, aliphatic and aromatic, have been selected as systems. Critical cases, e.g., C6H5CHCHCHO, CH3CHCHCHO, and CH2CHCHO, where a CC double bond is in conjugation with the CO group, are also considered. Two new reactivity descriptors are proposed, “relative electrophilicity” (sk+/sk-) and “relative nucleophilicity” (sk-/sk+), which will help to locate the preferable reactive sites. Our results show that local hardness can be used as a guiding parameter when constructing intermolecular reactivity sequences.Item Site of Protonation in Aniline and Substituted Anilines in the Gas Phase: A Study via the Local Hard and Soft Acids and Bases Concept(ACS, 1998-08-12) Roy, Ram KinkarIn this paper we address the long standing problem regarding the site for gas-phase protonation in aniline and substituted anilines. Our study reveals that DFT-based reactivity descriptors can reproduce the experimentally observed preferable protonation sites. However, it is found that the quantity / , termed “relative nucleophilicity” and a measure of “local polarizability”, produces more reliable results than the local softness, . The problem which sometimes arises in taking / as the reactivity descriptor is also discussed.