semiempirical

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semiempirically

　

WordNet

1. relying to some extent on observation or experiment

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/09/22 23:23:04」(JST)

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Electronic structure methods
Valence bond theory
Generalized valence bond Modern valence bond Resonance
Molecular orbital theory
Hartree–Fock method Semi-empirical quantum chemistry methods Møller–Plesset perturbation theory Configuration interaction Coupled cluster Multi-configurational self-consistent field Quantum chemistry composite methods Quantum Monte Carlo Linear combination of atomic orbitals
Electronic band structure
Nearly free electron model Tight binding Muffin-tin approximation Density functional theory k·p perturbation theory Empty lattice approximation
Book

Semi-empirical quantum chemistry methods are based on the Hartree–Fock formalism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large molecules where the full Hartree–Fock method without the approximations is too expensive. The use of empirical parameters appears to allow some inclusion of electron correlation effects into the methods.

Within the framework of Hartree–Fock calculations, some pieces of information (such as two-electron integrals) are sometimes approximated or completely omitted. In order to correct for this loss, semi-empirical methods are parametrized, that is their results are fitted by a set of parameters, normally in such a way as to produce results that best agree with experimental data, but sometimes to agree with ab initio results.

Semi-empirical methods follow what are often called empirical methods where the two-electron part of the Hamiltonian is not explicitly included. For π-electron systems, this was the Hückel method proposed by Erich Hückel. For all valence electron systems, the extended Hückel method was proposed by Roald Hoffmann.

Semi-empirical calculations are much faster than their ab initio counterparts, mostly due to the use of the zero differential overlap approximation. Their results, however, can be very wrong if the molecule being computed is not similar enough to the molecules in the database used to parametrize the method.

Semi-empirical calculations have been most successful in the description of organic chemistry, where only a few elements are used extensively and molecules are of moderate size. However, semi-empirical methods were also applied to solids and nanostructures but with different parameterization.

Empirical research is a way of gaining knowledge by means of direct and indirect observation or experience. As with empirical methods, we can distinguish methods that are:

• restricted to π-electrons. These method exist for the calculation of electronically excited states of polyenes, both cyclic and linear. These methods, such as the Pariser–Parr–Pople method (PPP), can provide good estimates of the π-electronic excited states, when parameterized well. Indeed, for many years, the PPP method outperformed ab initio excited state calculations.

or those:

• restricted to all valence electrons. These methods can be grouped into several groups:

• Methods such as CNDO/2, INDO and NDDO that were introduced by John Pople. The implementations aimed to fit, not experiment, but ab initio minimum basis set results. These methods are now rarely used but the methodology is often the basis of later methods.

• Methods that are in the MOPAC, AMPAC, and/or SPARTAN computer programs originally from the group of Michael Dewar. These are MINDO, MNDO, AM1, PM3, RM1[16] , PM6 and SAM1. Here the objective is to use parameters to fit experimental heats of formation, dipole moments, ionization potentials, and geometries.

• Methods whose primary aim is to predict the geometries of coordination compounds, such as Sparkle/AM1, available for lanthanide complexes.

• Methods whose primary aim is to calculate excited states and hence predict electronic spectra. These include ZINDO and SINDO.

the latter being by far the largest group of methods.

See also

• List of quantum chemistry and solid-state physics software

References

English Journal

• Nucleic acid reactivity: Challenges for next-generation semiempirical quantum models.

• Huang M1,2, Giese TJ2, York DM2.
• Journal of computational chemistry.J Comput Chem.2015 Jul 5;36(18):1370-89. doi: 10.1002/jcc.23933. Epub 2015 May 6.
• Semiempirical quantum models are routinely used to study mechanisms of RNA catalysis and phosphoryl transfer reactions using combined quantum mechanical (QM)/molecular mechanical methods. Herein, we provide a broad assessment of the performance of existing semiempirical quantum models to describe nu
• PMID 25943338

• Dehalogenation of persistent halogenated organic compounds: A review of computational studies and quantitative structure-property relationships.

• Luo J1, Hu J2, Wei X3, Fu L1, Li L1.
• Chemosphere.Chemosphere.2015 Jul;131:17-33. doi: 10.1016/j.chemosphere.2015.02.013. Epub 2015 Mar 9.
• Dehalogenation is one of the highly important degradation reactions for halogenated organic compounds (HOCs) in the environment, which is also being developed as a potential type of the remediation technologies. In combination with the experimental results, intensive efforts have recently been devot
• PMID 25765260

• Pyrrolyl-Silicon Compounds as Precursors for Donor-Acceptor Systems Stabilized by Noncovalent Interactions.

• González-Santana S1, Morera-Boado C1, Montero-Cabrera LA1, Trueba M2, Trasatti SP2.
• The journal of physical chemistry. A.J Phys Chem A.2015 Jun 29. [Epub ahead of print]
• Pyrrolyl-silicon compounds were investigated by different theoretical approaches. Model monomers consisted of a pyrrole ring N-substituted with silylmethoxy and silylhydroxy end groups through a propyl chain spacer, designated as PySi and PySiOH. Geometrical, vibrational, and electronic properties,
• PMID 26066388

Japanese Journal

• Hindered rotational physisorption states of H-2 on Ag(111) surfaces

• Physical chemistry chemical physics 17(29), 19625-19630, 2015-08-07
• NAID 120005649139

• HPGe検出器を用いる1000cm³マリネリビーカーに充填された環境試料定量のための実用的自己吸収補正手法

• RADIOISOTOPES 64(11), 661-671, 2015
• NAID 130005110109

• Thrust Performance of Rotary-Valved Four-Cylinder Pulse Detonation Rocket Engine

• TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES 58(4), 193-203, 2015
• NAID 130005083372

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