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![Occupations of natural orbitals for SnH,. MP2 and corresponding RAS B calculation * The MP2 calculation is done with frozen core orbitals: (1a,—3a,, le, 11.—3t,). Only the first NO with occupation less than 10~? is included in each symmetry. Table 6 For SnH, the MP2 NO occupation numbers indicate that an active space with 18 electrons distributed in 25 orbitals (5a,—7a,, 2e—3e, 1t,, 5t,-9t,) (corresponding to 5s, 5s’, 5p, Sp’, 4d, 4d’, 4f’ of the united atom, Xe), see Table 6. As in the case of GeH, it was not computationally feasible to use such large CAS space, and we performed instead a singles and doubles restricted active space (SD-RAS) calculation with the same active space [14]. It turned out that the inclusion of the 4d electrons in the active space made the variational procedure replace the 5s, Sp orbitals in the active space with the 4s, 4p orbitals, thus correlating the inner valence shell completely and not correlating the more important outer valence shell. In order to get a good description of the molecule we therefore had to add the 4s, 4p, 4s’, 4p’ orbitals to the active space, leading to the employed RAS B calculation which is a SD-RAS calculation with 26 electrons distributed in the 33 orbitals shown in Table 5, for a total of 24999 determinants. In order to estimate how much of the correlation contained in the CAS space is recovered in the SD- RAS calculation, we performed aSD-RAS calculation (RAS A) with the same active space as the CAS A calculation. We conclude this discussion of the correlated calculation by stating that we believe that all the selected active spaces are balanced, which is corroborated by the observation that neither singlet nor triplet instabilities were](https://figures.academia-assets.com/110832877/table_006.jpg)
Table 6 Occupations of natural orbitals for SnH,. MP2 and corresponding RAS B calculation * The MP2 calculation is done with frozen core orbitals: (1a,—3a,, le, 11.—3t,). Only the first NO with occupation less than 10~? is included in each symmetry. Table 6 For SnH, the MP2 NO occupation numbers indicate that an active space with 18 electrons distributed in 25 orbitals (5a,—7a,, 2e—3e, 1t,, 5t,-9t,) (corresponding to 5s, 5s’, 5p, Sp’, 4d, 4d’, 4f’ of the united atom, Xe), see Table 6. As in the case of GeH, it was not computationally feasible to use such large CAS space, and we performed instead a singles and doubles restricted active space (SD-RAS) calculation with the same active space [14]. It turned out that the inclusion of the 4d electrons in the active space made the variational procedure replace the 5s, Sp orbitals in the active space with the 4s, 4p orbitals, thus correlating the inner valence shell completely and not correlating the more important outer valence shell. In order to get a good description of the molecule we therefore had to add the 4s, 4p, 4s’, 4p’ orbitals to the active space, leading to the employed RAS B calculation which is a SD-RAS calculation with 26 electrons distributed in the 33 orbitals shown in Table 5, for a total of 24999 determinants. In order to estimate how much of the correlation contained in the CAS space is recovered in the SD- RAS calculation, we performed aSD-RAS calculation (RAS A) with the same active space as the CAS A calculation. We conclude this discussion of the correlated calculation by stating that we believe that all the selected active spaces are balanced, which is corroborated by the observation that neither singlet nor triplet instabilities were
Related Figures (7)
![* All exponents are for Sn. > Number of contracted Gaussian type orbitals, including the H basis set. © Derived from Ref. [25] by decontracting the outermost contracted s- and d-orbitals, and adding tight s-functions with exponents 419354 and 27764049.0. Basis sets and SCF energies (in hartree) for SnH, Table 2](https://figures.academia-assets.com/110832877/table_002.jpg)
![One-bond coupling constants for CH,, SiH,, GeH,, and SnH,. All results are in Hz * The active space of the CASSCF and RASSCF calculations are given in Table 5. > CH, calculations are from Ref. [4]. © The equilibrium value at r,= 1.0858 A obtained from an analysis of the temperature dependence of the couplings in CH, isotopomers [28]. 4 From Ref. [21]. Bram Ref [92]](https://figures.academia-assets.com/110832877/table_007.jpg)
![Geminal proton—proton coupling constants for CH,, SiH4, GeH,, and SnHy. All results are in Hz 4 The active spaces of the CASSCF and RASSCF calculations are given in Tables 5 and 6. > The experimental values may in the case where no sign is given explicitly be either positive or negative. The values are from tables in Ref. [22]. ° CH, calculations are from Ref. [4]. 4 No experimental value available.](https://figures.academia-assets.com/110832877/table_008.jpg)