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Okumaya devam et...
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| === Generalized VBT (GVB) === | === Generalized VBT (GVB) === |
| This was one of the first ''ab initio'' computational methods developed that utilized VBT. Using Coulson-Fischer type basis orbitals, this method uses singly-occupied, instead of doubly-occupied orbitals, as the basis set. This allows from the distance between paired electrons to increase during variational optimization, lowering the resultant energy. <ref name=":3" /> The total wavefunction is described by a single set of orbitals, rather than a linear combination of multiple VB structures. GVB is considered to be a user-friendly method for new practitioners. <ref name=":1" /> | This was one of the first ''ab initio'' computational methods developed that utilized VBT. Using Coulson-Fischer type basis orbitals, this method uses singly-occupied, instead of doubly-occupied orbitals, as the basis set. This allows from the distance between paired electrons to increase during variational optimization, lowering the resultant energy.<ref name=":3" /> The total wavefunction is described by a single set of orbitals, rather than a linear combination of multiple VB structures. GVB is considered to be a user-friendly method for new practitioners.<ref name=":1" /> |
| === Spin-coupled generalized valence bond theory (SCGVB, or sometimes SCVB/full GVB)<ref>{{Cite journal |last1=Dunning |first1=Thom H. |last2=Xu |first2=Lu T. |last3=Cooper |first3=David L. |last4=Karadakov |first4=Peter B. |date=2021-03-18 |title=Spin-Coupled Generalized Valence Bond Theory: New Perspect i ves on the Electronic Structure of Molecules and Chemical Bonds |url=https://pubs.acs.org/doi/10.1021/acs.jpca.0c10472 |journal=The Journal of Physical Chemistry A |language=en |volume=125 |issue=10 |pages=2021–2050 |doi=10.1021/acs.jpca.0c10472 |pmid=33677960 |s2cid=232143562 |issn=1089-5639}}</ref> === | === Spin-coupled generalized valence bond theory (SCGVB, or sometimes SCVB/full GVB)<ref>{{Cite journal |last1=Dunning |first1=Thom H. |last2=Xu |first2=Lu T. |last3=Cooper |first3=David L. |last4=Karadakov |first4=Peter B. |date=2021-03-18 |title=Spin-Coupled Generalized Valence Bond Theory: New Perspect i ves on the Electronic Structure of Molecules and Chemical Bonds |url=https://pubs.acs.org/doi/10.1021/acs.jpca.0c10472 |journal=The Journal of Physical Chemistry A |language=en |volume=125 |issue=10 |pages=2021–2050 |doi=10.1021/acs.jpca.0c10472 |pmid=33677960 |s2cid=232143562 |issn=1089-5639}}</ref> === |
| SCGVB is an extension of GVB that still uses delocalized orbitals, whose delocalization can adjust with molecular structure. In addition, the electronic wavefunction is still a single product of orbitals. The difference is that the spin functions are allowed to adjust simultaneously with the orbitals during energy minimization procedures. This is considered to be one of the best VB descriptions of the wavefunction that relies on only a single configuration. <ref name=":1" /> | SCGVB is an extension of GVB that still uses delocalized orbitals, whose delocalization can adjust with molecular structure. In addition, the electronic wavefunction is still a single product of orbitals. The difference is that the spin functions are allowed to adjust simultaneously with the orbitals during energy minimization procedures. This is considered to be one of the best VB descriptions of the wavefunction that relies on only a single configuration.<ref name=":1" /> |
| === Complete active space valence bond method (CASVB) === | === Complete active space valence bond method (CASVB) === |
| This is a method that often gets confused as a traditional VB method.<ref name=":1" /> Instead, this is a localization procedure that maps the full configuration interaction [[Hartree–Fock method|Hartree-Fock]] wavefunction ([[Multi-configurational self-consistent field|CASSCF]]) onto valence bond structures. <ref>D. L. Cooper, T. Thorsteinsson, J. Gerratt, Adv. Quant. Chem. 32, 51 (1998). Modern VB Representation of CASSCF Wave Functions and the Fully-Variational Optimization of Modern VB Wave Functions Using the CASVB Strategy.</ref> | This is a method that often gets confused as a traditional VB method.<ref name=":1" /> Instead, this is a localization procedure that maps the full configuration interaction [[Hartree–Fock method|Hartree-Fock]] wavefunction ([[Multi-configurational self-consistent field|CASSCF]]) onto valence bond structures.<ref>D. L. Cooper, T. Thorsteinsson, J. Gerratt, Adv. Quant. Chem. 32, 51 (1998). Modern VB Representation of CASSCF Wave Functions and the Fully-Variational Optimization of Modern VB Wave Functions Using the CASVB Strategy.</ref> |
| == Spin-coupled theory == | == Spin-coupled theory == |
| There are a large number of different valence bond methods. Most use n valence bond orbitals for n electrons. If a single set of these orbitals is combined with all linear independent combinations of the [[spin function]]s, we have '''spin-coupled valence bond theory'''. The total [[wave function]] is optimized using the [[variational method]] by varying the coefficients of the basis functions in the valence bond orbitals and the coefficients of the different spin functions. In other cases only a sub-set of all possible spin functions is used. Many valence bond methods use several sets of the valence bond orbitals. Be warned that different authors use different names for these different valence bond methods. | There are a large number of different valence bond methods. Most use ''n'' valence bond orbitals for ''n'' electrons. If a single set of these orbitals is combined with all linear independent combinations of the [[spin function]]s, we have '''spin-coupled valence bond theory'''. The total [[wave function]] is optimized using the [[variational method]] by varying the coefficients of the basis functions in the valence bond orbitals and the coefficients of the different spin functions. In other cases only a sub-set of all possible spin functions is used. Many valence bond methods use several sets of the valence bond orbitals. It is important to note here that different authors use different names for these different valence bond methods. |
| == Valence bond programs == | == Valence bond programs == |
Okumaya devam et...