This paper offers the first series of state-of-the-art quantum chemical calculations (CASSCF, CASPT2, MS-CASPT2) and analytical models for the well-known problem of quasi-general ferromagnetic coupling in copper-gadolinium complexes. A system chosen from the chemical report of Costes et al. was taken as prototype. At the CASSCF level, calculated results for the experimental structure reproduced the magnetic coupling constant well (J(calcd)( )()= +7.67 cm(-)(1) vs J(exp)( )()= +7.0 cm(-)(1)). For more insight, the study molecule was further idealized by geometry optimization to C(2)(v)() symmetry. Systematic ab initio computation experiments were designed and performed. Owing to specific problems related to the non-aufbau ground configuration of the [CuL-Gd] complexes, the calculations were conducted in a nonstandard manner. We found that the qualitative mechanism of Kahn, assigned to the electron jump from 3d of Cu(II) to 5d shell of Gd(III), can be presented effectively as the cause of the phenomenon, if CASPT2 MOs are taken as magnetic orbitals. We showed that the ferromagnetic coupling is also matched and magnified by spin polarization effects over the ligand, in line with the early assumption of Gatteschi. To be distinguished from the initial hypothesis of Gatteschi, which assumed the role of 6s AO of Gd(III), we found that one 5d-type AO is actually involved in the polarization scheme. In fact, the Gatteschi and Kahn mechanisms are not mutually contradictory, but are even interconvertible with appropriate changes of the magnetic orbitals. Within C(2)(v)() symmetry of complexes, the ferromagnetic coupling can be qualitatively regarded as the preponderant influence of interaction channels exhibiting orbital orthogonality (four 3d-4f contacts) over the nonorthogonal ones (two 3d-4f contacts). The effective preponderance from ferromagnetic pathways is supported by CASPT2 results. One may explain the generality of Cu(II)-Gd(III) ferromagnetic coupling as being correlated with the large occurrence of approximate pseudo-C(2)(v)() geometry of complexes. The observed orbital regularity is lost in lower symmetries. Thus, the antiferromagnetic exceptions occur when the molecular asymmetry is advanced (e.g., owing to strong chemical nonequivalence of the donor atoms).

We report on the performance of the third-order Douglas–Kroll ab initio model potential (DK3-AIMP) method-based electron-correlated spin–orbit calculations. Our treatment assumes that the problem can be separated into a spin–free correlation treatment and a spin–orbit calculation. The correlation effects were calculated using the multistate complete active space second-order perturbation method, and the spin–orbit effects were treated by means of the restricted active space state interaction spin–orbit method, where the spin–orbit effects were approximated by the Douglas–Kroll type of atomic mean-field spin–orbit method. We used our method for illustrative calculations on the ground and low-lying electronic states of thorium monoxide. For a proper description of the inner core region in the spin–orbit calculations, an auxiliary spin–orbit basis set was introduced. The DK3-AIMP-based electron-correlated spin–orbit calculations on ThO yield good agreement with corresponding all-electron results and with the available experimental data. This confirms that the DK3-AIMP method can be easily combined with highly accurate correlation treatments and relativistic effects, both of which are vital for studying the actinides. To our knowledge, the literature contains no references to AIMP calculations on the low-lying states of ThO.

The U + O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO + .Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U + O → UO + + e − is proposed. The U + O and Sm+ O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions to be studied theoretically in this way.

Density functional theory based global and local electrophilicity descriptors are used to study the reliability of local electrophilicity values of the strongest electrophilic sites in generating global intermolecular electrophilicity trends. The evaluated values on 15 different organic chlorides show that, for systems having more than one comparatively strong electrophilic site, the local electrophilicity value of the strongest site does not produce a reliable global intermolecular electrophilicity trend. But for systems having one distinctly strong electrophilic site it does. The analytical explanation in favor of the above observation is also provided. Thus, what was argued in an earlier study (Roy, R. K. J. Phys. Chem. 2004, 108, 4934) is established strongly by numerical demonstrations as well as analytical reasoning in the present one.

Articles you may be interested inModel core potentials of p-block elements generated considering the Douglas-Kroll relativistic effects, suitable for accurate spin-orbit coupling calculations Correlated ab initio calculations of spectroscopic parameters of SnO within the framework of the higher-order generalized Douglas-Kroll transformation Accurate relativistic Gaussian basis sets determined by the third-order Douglas-Kroll approximation with a finitenucleus model Erratum: "Ab initio relativistic effective potentials with spin-orbit operators. VII. Am through element 118" [J.A relativistic ab initio model potential ͑AIMP͒ method with the third-order Douglas-Kroll ͑DK3͒ approximation has been developed for the whole series of the actinide elements from Th to Lr. Two different cores, i.e., ͓Xe, 4 f ,5d] and ͓Xe, 4 f ], have been employed and the corresponding valence basis sets, (14s10p11d9 f )/͓6s5 p5d4 f ͔ and (14s10p12d9 f )/͓6s5 p6d4 f ͔, are presented for all actinides. The mean absolute errors of the AIMP relative to the all-electron results for the atomic SCF valence orbital energies ͑⑀͒ and the radial expectation values (͗r͘) are 0.003 ͑0.001͒ hartree and 0.004 ͑0.006͒ bohr with the small ͑large͒ core set. The spectroscopic properties of the 1 ⌺ ϩ ground state of thorium monoxide, ThO, are calculated at the SCF and complete active space SCF levels. The DK3-AIMP results again satisfactorily reproduce the all-electron DK3 results. The large core set gives almost the same results as the small set for atomic and molecular calculations, suggesting that the 5d electrons can safely be omitted from the valence electrons in actinide chemistry.

The SmϩO chemiionization reaction has been investigated theoretically using a method that allows for correlation and relativistic effects. Potential energy curves have been calculated for several electronic states of SmO and SmO ϩ . Comparison with available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemiionization reaction SmϩO is proposed. The importance of spin-orbit coupling in the excited states of SmO, in allowing this chemiionization reaction to take place, has been revealed by these calculations. This paper shows the metal-plus-oxidant chemiionization reaction.