Calculations, density functions

J Li, L Noodleman, DA Case. Electronic structure calculations Density functional methods with applications to transition metal complexes. In EIS Lever, ABP Lever, eds. Inorganic Electronic Structure and Spectroscopy, Vol. 1. Methodology. New York Wiley, 1999, pp 661-724. 

The calculated density functional KS-LCAO energy is denoted E(RB-LYP). 

Li, J., Noodleman, L., Case, D.A. Electronic stmcture calculations Density functional methods with applications to transition metal complexes. In Solomon, E.I., Lever, A.B.P. (eds.) Inorganic Electronic Stmcture and Spectroscopy, vol. 1, P- 661. Wiley, New York (1999)... 

Carbon-carbon bond lengths for a selection of hydrocarbons obtained from molecular mechanics calculations, Hartree-Fock calculations, local density calculations, density functional calculations, MP2 calculations and semi-empirical calculations are compared with experimental distances in Table 5-3. The same basis sets considered for main-group hydrides are utilized here. Mean absolute errors for each method have also been tabulated. 

Density functional calculations (DFT calculations, density functional theory) are, like ab initio and semiempirical calculations, based on the Schrodinger equation However, unlike the other two methods, DFT does not calculate a conventional wavefunction, but rather derives the electron distribution (electron density function) directly. Afunctional is a mathematical entity related to a function. 

Compared to other methods (molecular mechanics, semiempirical calculations, density functional calculations - Chapters 3, 6 and 7, respectively) ab initio calculations are slow, and they are relatively demanding of computer resources (memory and disk space, depending on the program and the particular calculation). These disadvantages, which increase with the level of the calculation, have been to a very large extent overcome by the tremendous increase in computer power, accompanied by decreases in price, that have taken place since the invention of electronic computers. In 1959 Coulson doubted the possibility (he also questioned the desirability, but in this regard visualization has been of enormous help) of calculations on molecules with more than 20 electrons, but 30 years later computer speed had increased by a factor of 100,000 [329], and ab initio calculations on molecules with 100 electrons (about 15 heavy atoms) are common. 

Recently, another class of calculations, density functional theory (DFT) has become quite common. This method is faster than ab initio calculations for similar levels of performance, and has the advantage that correlation effects are included, at least in part. According to this theory, the properties of a molecular system are functions of the electron density, rather than a wave function (as described by the Schrodinger equation). There is some degree of debate over whether DFT is an ab initio calculation or in a class by itself. Parenthetically, one of the recipients of the 1998 Nobel Prize for Chemistry was Walter Kohn, in recognition of his development of density functional theory. 

As an alternative to Hartree-Fock semiempirical and ab initio calculations, density functional theory has been used to obtain nonlinear optical properties in both the finite field and TDHF > (or time-dependent Kohn-Sham) approaches. 

Wu, Q., and Yang, W. A direct optimization method for calculating density functionals and exchange-correlation potentials from electron densities./ Chem. Phys., 118, 2498-2509, doi doi 10.1063/1.1535422 (2003). 

Keywords Silyl Cations / Ab Initio Calculations / Density Functional Calculations / NMR Spectroscopy / Silanorbomenes / Silanorbomadienes... 

Theoretical calculations Density functional theory 50 upstroke 30 downstroke 1991 [125]... 

Li, J. Noodleman, L. Electronic Structure Calculations Density Functional Methods for Spin Polarization, Charge Transfer and Solvent Effects in Transition Metal Complexes. In Solomon, E. I. Hodgson, K. O., Ed., ACS Symposium Series 692 Spectroscopic Methods in Bioinorganic Chemistry, American Chemical Society Washington, DC 1998, pp 179-197. 

Rai, B., Krishnamurty, S., Sathish, R, and Pradip. 2008a. Salicylaldoxime derivatives as flotation collectors Quantum mechanics calculations (density functional theory) for the design of selective reagents. In Proceedings of Mineral Processing Technology—2008, IIME, Trivandrum, India. 

Calculating Density Functionals and Exchange-Correlation Potentials from Electron Densities. 

Combined Quantum Mechanical and Molecular Mechanical Potentials Combined Quantum Mechanics and Molecular Mechanics Approaches to Chemical and Biochemical Reactivity Configuration Interaction Configuration Interaction Semiempirical Calculations Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Force Fields A General Discussion Hybrid Methods MNDO Quantum Mechanical/Molecular Mechanical (QM/MM) Coupled Potentials Quantum Mecha-nics/Molecular Mechanics (QM/MM). 

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