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The reliability of the continuous transformations of origin of the current density method, which makes the transverse paramagnetic current vanish (CTOCD-PZ), for the prediction of nearly gauge-origin independent molecular magnetic susceptibility and gauge-origin independent nuclear magnetic shielding, is proved on the basis of a fairly large number of calculations. It is shown that, within the computational scheme provided by the coupled Hartree–Fock perturbation theory (CHF), convergence towards the presumed Hartree–Fock limit, for magnetic susceptibility and proton magnetic shielding, is systematically reached using basis sets which are smaller than those required by conventional common origin and CTOCD-DZ techniques. For second-row nuclear magnetic shieldings a variant of the CTOCD-PZ method, which shifts the origin of the current towards the nearest nucleus for points close to nuclei, as suggested originally by Keith and Bader with the CSDGT method [T. A. Keith and R. F. W. Bader, Chem. Phys. Lett. 210, 223 (1993)], gives likewise good results with affordable basis sets.

Articles you may be interested inNon-perturbative calculation of molecular magnetic properties within current-density functional theory Gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach. II. Density functional and coupled cluster theory J. Chem. Phys. 126, 154111 (2007); 10.1063/1.2721536Correlated and gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach Calculation of third-rank molecular hypermagnetizabilities by continuous transformation of the origin of the current density Coupled Hartree-Fock calculations of molecular magnetic properties annihilating the transverse paramagnetic current density A new method for the calculation of molecular magnetic susceptibility and nuclear magnetic shielding is presented. It is based on continuous transformations of origin of the current density which make the transverse part of the paramagnetic current vanish. For any molecule all the components of the nuclear magnetic shielding tensor provided by the new method are independent on the origin of the gauge, whereas the components of the magnetizability tensor are translationally invariant only for center-symmetric molecules ͑they, in general, show a linear dependence on the shift of origin͒. This method, termed CTOCD-PZ, has been implemented for the theoretical determination of molecular magnetic properties via numerical integration techniques and, from preliminar results obtained for methane and carbon dioxide molecules, reveals reliable.

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In this paper, both Hartree-Fock (HF) and density functional theory (DFT) methods have been used to make ab initio calculations of the optical rotatory power of selected molecules at several wavelengths; that is, part of the optical rotatory dispersion (ORD) curve has been predicted. This approach constitutes a new, simple, and reliable method to assign the molecular absolute configuration, at least for rigid molecules such as those studied in the present work. In fact, in this way, it is possible to overcome the difficulties connected to some relevant cases, in particular that of (-)-beta-pinene, for which even a very high-level (DFT/B3LYP/6-311++G(2d,2p)) calculation affords the wrong sign of the optical rotation at 633 nm. On the contrary, the predicted ORD curve, even using small basis sets, reproduces (below 400 nm) the experimental trend well, allowing for the correct configurational assignment. This result clearly shows that to have a reliable configurational assignment the comparison between experimental and predicted rotation values must be carried out at different wavelengths and not at a single frequency. The reason for this is that working at wavelengths approaching the absorption maximum the [alpha](lambda) values become larger and their prediction becomes more reliable. Coupling the use of an inexpensive instrument (a polarimeter working at a few wavelengths) with the use of a DFT-calculation package can also allow the experimental organic chemist to arrive, quickly and reliably, at the assignment of the molecular absolute configuration.