Chemistry is the study of matter - its composition, structure, properties, and changes. With new substances discovered daily, the field offers vast knowledge to explore. Chemists use various methods to identify, classify, and name unknown substances. In modern laboratories, scientists closely study organic molecules, their functional groups, identification methods, and their properties and relationships. 

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Computational quantum chemistry is a branch of theoretical chemistry that employs computational methods to solve the Schrödinger equation, which describes the behavior of electrons in atoms and molecules. This field aims to predict molecular properties and behaviors based on quantum mechanical principles.

Quantum chemistry calculations typically involve solving the Schrödinger equation either directly or through approximate methods due to the complexity of many-electron systems. These calculations can provide insights into various molecular properties such as electronic structure, molecular geometry, bond energies, reaction mechanisms, and spectroscopic properties.

Several computational methods are used in quantum chemistry, including:

1. Ab initio methods: These methods solve the Schrödinger equation without using any experimental data or empirical parameters. Examples include Hartree-Fock (HF) theory, post-Hartree-Fock methods like Møller-Plesset perturbation theory (MPn), and coupled cluster (CC) methods.

2. Density functional theory (DFT): DFT is a widely used method that treats electrons in terms of their electron density rather than as individual particles. It's computationally more efficient than many ab initio methods and is often used for studying large systems.

3. Semi-empirical methods: These methods combine elements of both ab initio and empirical approaches. They use some experimental data and empirical parameters to simplify calculations. Examples include the AM1, PM3, and PM6 methods.

4. Molecular mechanics: While not strictly quantum mechanical, molecular mechanics methods use classical mechanics to model molecular systems, approximating atomic interactions using force fields.

Quantum chemistry calculations are vital in various fields such as drug design, materials science, catalysis, and atmospheric chemistry. They help in understanding molecular behavior at a fundamental level and aid in the design and optimization of molecules with desired properties.

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1. π and σ-phenylethynyl radicals and their isomers o-, m- and p-ethynylphenyl: Structures, energetics, and electron affinities, Raj K. Sreeruttun, Ponnadurai Ramasami, Chaitanya S. Wannere, Andrew C.Simmonett, and Henry F. Schaefer III, Phys. Chem. A (2008) 2838-2845. Link

2. Conformational behaviour of 1,2-dichloroethane and 1,2-dibromoethane: 1HNMR, IR, refractive index and theoretical studies, Raj K. Sreeruttun and Ponnadurai Ramasami, Physics and Chemistry of Liquids 44 (2006) 315-328. Link 

3. Effects of fluorine on the structures and energetics of propynyl and propargyl radicals and their anions, Raj K. Sreeruttun, Ponnadurai Ramasami, Ankan Paul, Chaitanya S. Wannere, Paul v. R. Schleyer and Henry F. Schaefer, J. Org. Chem. 70 (2005) 8676-8686. Link

4. The alkylethynyl radicals, .C≡C-CnH2n+1 and their anions, Raj K. Sreeruttun, Ponnadurai Ramasami, Ge Yan, Chaitanya S. Wannere, Paul v. R. Schleyer and Henry F. Schaefer, J. of Mass Spectrometry 241 (2005) 295-304. Link

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