Semiempirical calculations, for

Figure 12. Electronic spectra and the results of open-shell PPP-like semiempirical calculations for radical ions. The vertical lines represent the allowed transitions, the wavy lines with arrows the forbidden ones. The right side scales denote the calculated spectral intensities, where f stands for the oscillator strength. Top left the absorption curve (146) redrawn to the log e vs. 0 (cm ) form calculations are taken from (59). Top right taken from (11). Bottom left taken from (143). Bottom right taken from (136), the absorption curve redrawn to the log e vs, 0 (cm" ) form.

The manifestation of a Mills-Nixon effect in benzocyclopropene (1) was examined by a variety of methods. Thus examination of the PE spectra of cyclo-proparenes and appropriate model compounds provided no information on the question.Similarly, NMR investigations using vicinal coupling constants or orthobenzylic coupling constants, involving methyl-substituted cydoproparenes revealed no evidence for sterically induced bond fixation. Theoretical calculations led to contradictory results. Early extended Hiickel calculations supported the concept in indanes but in the opposite sense than that suggested by Mills and Nixon. Semiempirical calculations for benzocyclopropene favored structure 258 over A substantial Mills-Nixon effect in the same direction resulted from... 

Step 3 is a geometry optimization. Appropriate keywords might be CASSCF (2,2)/6-31G, specifying a CASSCF(2,2) procedure (a limited Cl optimization) using the 6-31G basis, which will normally be the smallest chosen. Other keywords might dictate the information to be taken from step 2 and how to calculate the initial Hessian (e.g., use a semiempirical calculation) for the optimization. Figure 8.11 compares our CASSCF(2,2)/6-31G C2h relative minimum (no imaginary frequencies - see below) with the C2h CASSCF(4,4)/6-31G minimum of Doubleday [61]. 

The electronic states of rare earth ions in crystals are N-body localized states, since the N electrons of 4fN are coupled strongly, and move around the corresponding ion core without extending far away. The semiempirical calculations for the 4fx energy level systems employ a parametrized Hamiltonian H under the appropriate site symmetry for Ln3+ ... 

The photochemical model was probed by using one triazene polymer (structure shown in Scheme 5). Semiempirical calculations for a model compound, i.e., a bis-triazene (shown in Scheme 7) were applied to determine a realistic number of chromophores, which results in a decreasing number of free fitting parameters. 

The boric acid complexes of a-pyridoin have recently been investigated using semiempirical calculations. For AM 1-optimized structures, spectroscopic parameters were calculated by CNDO/S and INDO/S methods and a good agreement with observed values was found <93JPC8602>. 

The properties of oligomers of thiophene at the ground and excited states have been investigated by semiempirical and ab initio methods. Semiempirical calculations for the ground state of thiophene involve the QCFF/PI - - CISD method <94JCP(100)2571>, while ab initio calculations are carried out at the Hartree-Fock/6-31G and the CASSF/3-21G levels <94jcp(100)2571> and also at the SCF and the ACPF levels, with (basis set I) and without (basis set II) the sulfur 3(/-orbitals <92JST(259)l8i>. 

Gurikov [Gu 80] developed semiempirical calculations for the characterization of solvent polarity. His method has, however, a limited use. 

Campos-Vallette, M.M., R.E. Clavijo, RE. Mendizabal, G. Diaz Fleming, J. Costamagna, J. Canales, and J. Vargas (1997). Vibrational study and semiempirical calculation for the hexaazacyclophane copper(II) complex. Vib. Spectrosc. 14, 71. 

Holder, A. J. Ward. R. White. D. A. Jie. C. SAMI semiempirical calculations for iron and selected other first row transition metals. Book of Abstracts, 216th ACS National Meeting, Boston, August 23-27 (1998), COMP-174, American Chemical Society Washington, DC. 

Semiempirical calculations for j or AEf were carried out by the SCF-MO method with integral approximations [23], by various versions of the CNDO [24 to 27] and INDO [1 to 4, 28] methods, by the MNDO method [29], by the extended Huckel and Pariser-Parr-Pople methods [30], and by a simple [31] MO method [32]. 

Using an available computational chemistry program, carry out a semiempirical calculation for the carbonate ion, COj . Compare your LCAOMOs with those obtained by the simple guesswork LCAOMO analysis. 

The main importance of Cl is that the FCI calculations provide results that are used as benchmarks for testing other post-Hartree-Fock methods. Less important seems to be the use of Cl as a post-Hartree-Fock method in routine chemical applications, because results of about the same accuracy may be obtained more economically by other methods. The size inconsistency of CI-SD may also be a drawback in some applications. Still, the recent progress in the development of Cl programs indicates that Cl might regain its importance even in this field. The traditional domain of Cl has been in electronic spectroscopy and excited electronic states in general. This is still true for semiempirical calculations. For ab initio calculations, however, it may be preferable to use multi-reference second-order perturbation theory, SAC-CI, or the equation-of-motion CC approach. 

Churio MS, Angermund KP and Braslavsky SE (1994) Combination of laser-induced optoacoustic spectroscopy (LIOAS) and semiempirical calculations for the determinations of molecular volume changes the photoisomerization of carbocyanines. Journal of Physical Chemistry 98 1776-1782. 

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