As in Sect.6.1, comparison with SCF and full-CI curves (the latter, even with frozen Is cores, involving almost 10 million Slater determinants), testifies to the adequacy of the description in terms of three VB structures, the reduced energy curve being in excellent agreement with that from the full-CI calculation. [Pg.396]

There exists, however, a cheap procedure which can be used to improve convergence toward second order with very little extra cost. This procedure also automatically reintroduces the Cl- coupling term, which is normally left out in super-CI calculations. [Pg.229]

For /2(Ar)i7, an extensive CI-CSP simulation was carried out, and the results were compared with those of the simple CSP approximation. Both calculations are for the ultrafast dynamics following excitation of the I2 into the B state. We found that the CI-CSP calculation, including doubly excited configurations , is close to converged for times up to t 500 fs, when 1500 configurations are included. Fig. 2 shows co(t)p, the coefficient of the CSP term and the doubly excited terms in the full CI-CSP wavefunction, [Pg.373]

The data shown in Table 19 suggest that the observed spectral transitions of cytosine in water can be explained in terms of the scaled transition energies of the hydrated keto-NlH tautomer within the accuracy of about 0.2 eV except the second transition. However, the error becomes smaller if a comparison is made between the computed transitions of the hydrated keto-NlH tautomer and the observed transitions of the cytosine sublimed film. ° Such a difference between the computed and experimental data is not unexpected since the general features of the cytosine spectrum are found to be solvent dependent. It appears that the absorption peak of cytosine in water near 212 nm (5.85 eV) is shifted to 6.07 eV in the sublimed film experiment. The suggested splitting of the 197 nm (6.29 eV) transition in the form of 202 and 189 nm (6.14 and 6.56 eV, respectively) bands found in CD experiments is neither revealed in the CIS calculations nor in the [Pg.313]

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