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【求助】请教两种基组的区别
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请教两种基组的区别 分别是HF/6-31G* 和 B3LYP/cc-pVTZ 感谢解惑 |
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S07111072
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2楼2009-03-04 08:16:46
erylingjet
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lei0736(金币+4,VIP+0):谢谢 3-4 10:33
lei0736(金币+4,VIP+0):谢谢 3-4 10:33
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The most common type of ab-initio calculation is called Hartree-Fock calculation(abbreviated HF), in which the primary approximation is called the mean field approximation. This means that the Coulombic electron-electron repulsion is not explicitly taken into account, however, its average effect is included in the calculation. This is a variational calculation, which implies that the approximate energies calculated are all equal to or greater than the exact energy. The accuracy of the calculation depends on the size of the basis set used, however because of the mean field approximation, the energies from HF calculations are always greater than the exact energy and tend, with increasing basis size, to a limiting value called the Hartree-Fock limit.  An alternative ab-initio method is Density Functional Theory (DFT), in which the total energy is expressed in terms of the total electron density, rather than the wavefunction. This type of calculation leads to an approximate effective or model Hamiltonian and to an approximate expression for the total electron density. Often the electron density approximations are made using some empirical corrections. Such DFT approaches are related to semi-empirical methods |
3楼2009-03-04 08:20:36
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4楼2009-03-04 08:28:53
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5楼2009-03-04 11:36:09