Ionization Potential Calculations

Until now, applications of semiempirical all-valence-electron methods have been rare, although the experimental data for a series of alkyl radicals are available (108,109). In Figure 9, we present the theoretical values of ionization potentials calculated (68) for formyl radical by the CNDO version of Del Bene and Jaffe (110), which is superior to the standard CNDO/2 method in estimation of ionization potentials of closed-shell systems (111). The first ionization potential is seen, in Figure 9, to agree fairly well with the experimental value. Similarly, good results were also obtained (113) with some other radicals (Table VII). 

The ionization potential calculated by MOP AC seemed to be capable of correcting the log k values of polychlorobenzenes when alkylbenzenes were used as standards, as shown in Figure 6.5 where the ionization potentials of alkyl and polychlorobenzenes are shown. 

Ionization potentials calculated for cyclopentadienide ions (1 -8 ) by a semi-empirical molecular-orbital method (AMI) correlate with the observed electron... 

The lone-pair ionization potentials calculated according to Nakajima and Pullman.281... 

The values of the ionization potentials of a few minor pyrimidine bases were estimated from the charge transfer spectra255 (Table XXXIII). These values compare well with the ionization potentials calculated by means of the 77-SCF MO method.156 However, the relative order of the ionization potentials given by the calculations (77-SCF MO and CNDO/2 methods, Tables XXXIII and XXXIV)—thiocytosine... 

Ionization potentials calculated by the ASCF24 method were studied by Guest and Saunders,29 who found that this combined SCF procedure successfully accounts for the relaxation energies computed by independent ASCF calculations. 

Methylation of cytosine residues within CpG dinucleotides is important in the regulation of genes. The interest in 5-MeCytosine results from its low ionization potential. It would be very interesting to continue the work on GG stacks (Section 18.6.4) by including 5-MeCytosine in the ionization potential calculations. 

A value of the vertical ionization potential calculated" using the energy difference method at the MP3/6-311G level, 9.5 eV, is in excellent agreement with the observed value. 

Several physical-chemical properties of alkanes, polyaromatic hydrocarbons, alkylben-zenes, polychlorobenzenes, polymethylphenols and polychlorophenols were determined using various software packages. The ionization potentials calculated by the MOPAC program was the most suitable property with which to adjust the capacity ratios of polychlorobenzene, polymethylphenol and polychlorophenol isomers . 

The EDM ionization potential calculations discussed in Sections III.A and III.B include some numerically important third-order terms while neglecting other third-order terms whose importance is suggested by means of the various comparisons. In this section we investigate these remaining third-order contributions in EOM IP calculations. 

Shifted Versus Unshifted Denominators in EOM Ionization Potential Calculations for N2 Using Simons Basis ... 

Figure 6. The variation in the measured ionization potential of mercury clusters as a function of cluster size. The work function for bulk Hg (4.49 eV) is indicated. The dashed line is a plot of the ionization potential calculated for the classical (liquid drop) electrostatic model for a metalUc sphere of diameter d. Region III contains clusters which are classified as insulating. Region II denotes the size-induced metal-insulator transition, in which overlap of the 6s and 6p states sets in at around Hgn. The larger clusters, located in Region I, have valence electronic structures that closely resemble the band structures of liquid and crystalline mercury. Adapted from Rademann. i...

Density functional calculations in which the exchange-correlation effects are treated beyond the LDA give the hope that Eq. (21) will be fulfilled better. This has been achieved to a large extent by the so called non-local weighted-density-approximation (WDA) [24, 29]. The results are also given in Table 2. IchomoI is very close to the experimental ionization potential and also rather close to the WDA ionization potential calculated from Eq. (20). The original paper [30] should be consulted for details. 

Table 10.1 lists the total energy values for the Cu atom, Cu cation, and CuH molecule. The experimental and calculated ionization potentials (IPs) of Cu are summarized in Table 10.2. The ionization potential calculated with corrected wave functions are 0.261(41) a.u. The ZORA-VMC calculation improves the analytical ZORA-HF result (0.242 a.u.) because of the inclusion of the electron correlation, but it only recovers about half of the correlation energy. This insufficient inclusion of the correlation energy will be improved by the ZORA-DMC method. We will investigate the improvements obtained by the relativistic DMC treatment in a future work.

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