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Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of molecules, groups of molecules, and solids. It is essential because, apart from relatively recent results concerning the hydrogen molecular ion, the quantum many-body problem cannot be solved analytically, much less in closed form. While computational results normally complement the information obtained by chemical experiments, it can in some cases predict hitherto unobserved chemical phenomena. It is widely used in the design of new drugs and materials.
Sir John Anthony Pople was a British theoretical chemist who was awarded the Nobel Prize in Chemistry with Walter Kohn in 1998 for his development of computational methods in quantum chemistry.
Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions to physical and chemical properties of molecules, materials, and solutions at the atomic level. These calculations include systematically applied approximations intended to make calculations computationally feasible while still capturing as much information about important contributions to the computed wave functions as well as to observable properties such as structures, spectra, and thermodynamic properties. Quantum chemistry is also concerned with the computation of quantum effects on molecular dynamics and chemical kinetics.
In chemistry, molecular orbital theory is a method for describing the electronic structure of molecules using quantum mechanics. It was proposed early in the 20th century.
Q-Chem is a general-purpose electronic structure package featuring a variety of established and new methods implemented using innovative algorithms that enable fast calculations of large systems on various computer architectures, from laptops and regular lab workstations to midsize clusters and HPCC, using density functional and wave-function based approaches. It offers an integrated graphical interface and input generator; a large selection of functionals and correlation methods, including methods for electronically excited states and open-shell systems; solvation models; and wave-function analysis tools. In addition to serving the computational chemistry community, Q-Chem also provides a versatile code development platform.
In theoretical and computational chemistry, a basis set is a set of functions that is used to represent the electronic wave function in the Hartree–Fock method or density-functional theory in order to turn the partial differential equations of the model into algebraic equations suitable for efficient implementation on a computer.
MNDO, or Modified Neglect of Diatomic Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Diatomic Differential Overlap integral approximation. Similarly, this method replaced the earlier MINDO method. It is part of the MOPAC program and was developed in the group of Michael Dewar. It is also part of the AMPAC, GAMESS (US), PC GAMESS, GAMESS (UK), Gaussian, ORCA and CP2K programs.
Austin Model 1, or AM1, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation. Specifically, it is a generalization of the modified neglect of differential diatomic overlap approximation. Related methods are PM3 and the older MINDO.
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The fragment molecular orbital method (FMO) is a computational method that can compute very large molecular systems with thousands of atoms using ab initio quantum-chemical wave functions.
Gabedit is a Graphical User Interface to GAMESS (US), Gaussian, MOLCAS, MOLPRO, MPQC, OpenMopac, PC GAMESS, ORCA and Q-Chem computational chemistry packages.
Quantum chemistry composite methods are computational chemistry methods that aim for high accuracy by combining the results of several calculations. They combine methods with a high level of theory and a small basis set with methods that employ lower levels of theory with larger basis sets. They are commonly used to calculate thermodynamic quantities such as enthalpies of formation, atomization energies, ionization energies and electron affinities. They aim for chemical accuracy which is usually defined as within 1 kcal/mol of the experimental value. The first systematic model chemistry of this type with broad applicability was called Gaussian-1 (G1) introduced by John Pople. This was quickly replaced by the Gaussian-2 (G2) which has been used extensively. The Gaussian-3 (G3) was introduced later.
The polarizable continuum model (PCM) is a commonly used method in computational chemistry to model solvation effects. If it were necessary to consider each solvent molecule as a separate molecule, the computational cost of modeling a solvent-mediated chemical reaction would grow prohibitively high. Modeling the solvent as a polarizable continuum, rather than individual molecules, makes ab initio computation feasible. Two types of PCMs have been popularly used: the dielectric PCM (D-PCM) in which the continuum is polarizable and the conductor-like PCM (C-PCM) in which the continuum is conductor-like similar to COSMO Solvation Model.
References
- ↑ Gallup, Gordan A. (2002). Valence Bond Methods - Theory and applications. Cambridge: Cambridge University Press. ISBN 978-0-521-80392-2.
- ↑ van Lenthe, J. H.; Dijkstra, F.; Havenith, R. W. A. TURTLE - A gradient VBSCF Program Theory and Studies of Aromaticity. In Theoretical and Computational Chemistry: Valence Bond Theory; Cooper, D. L., Ed.; Elsevier: Amsterdam, 2002; Vol. 10; pp 79--116.
- 1 2 Li, Jiabo; McWeeny, Roy (2002). "VB2000: Pushing valence bond theory to new limits". International Journal of Quantum Chemistry. 89 (4): 208–216. doi:10.1002/qua.10293.
- ↑ Song, Lingchun; Mo, Yirong; Qianer, Zhang; Wu, Wei (1969). "XMVB: A program for ab initio nonorthogonal valence bond computations". Journal of Computational Chemistry. 17 (2): 197–204. doi:10.1080/00268976900100941.
- ↑ Zhenhua, Chen; Ying, First; Chen, Xun; Song, Jingshuai; Su, Peifeng; Song, Lingchun; Mo, Yirong; Qianer, Zhang; Wu, Wei (2015). "XMVB 2.0: A new version of Xiamen valence bond program". International Journal of Quantum Chemistry. 115 (11): 731–737. doi:10.1002/qua.24855.
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