Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree–Fock, Kohn–Sham, multiconfigurational self-consistent-field, Møller–Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms.

Liquid state 1H and 19F NMR experiments in the temperature range between 110 and 150 K have been performed on mixtures of tetrabutylammonium fluoride with HF dissolved in a 1:2 mixture of CDF3 and CDF2Cl. Under these conditions hydrogen bonded complexes between F− and a varying number of HF molecules were observed in the slow proton and hydrogen bond exchange regime. At low HF concentrations the well known hydrogen bifluoride ion [FHF]− is observed, exhibiting a strong symmetric H‐bond. At higher HF concentrations the species [F(HF)2]−, [F(HF)3]− are formed and a species to which we assign the structure [F(HF)4]−. The spectra indicate a central fluoride anion which forms multiple hydrogen bonds to HF. With increasing number of HF units the hydrogen bond protons shift towards the terminal fluorine's. The optimized gas‐phase geometries of [F(HF)n]−, n = 1 to 4, calculated using ab initio methods confirm the D∞h, C2v, D3h and Td symmetries of these ions. For the first time, both one‐bond couplings between a hydrogen bond proton and the two heavy atoms of a hydrogen bridge, here 1JHF and 1JHF where |1JHF|≥|1JHF'|, as well as a two‐bond coupling between the heavy atoms, here 2JFF, have been observed. The analysis of the differential width of various multiplet components gives evidence for the signs of these constants, i.e. 1JHF and 2JSF>0, and 1JHF|. <0. Ab initio calculations of NMR chemical shifts and the scalar coupling constants using the Density Functional formalism and the Multi‐configuration Complete Active Space method show a reasonable agreement with the experimental parameters and confirm the covalent character of the hydrogen bonds studied.

Articles you may be interested inCurrent density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. I. Dihydro-pyrrolo-pyrrole isomers Natural chemical shielding analysis of nuclear magnetic resonance shielding tensors from gauge-including atomic orbital calculations Ab initio, symmetry-coordinate and internal valence coordinate carbon and hydrogen nuclear shielding surfaces for the acetylene molecule are presented. Calculations were performed at the correlated level of theory using gauge-including atomic orbitals and a large basis set. The shielding was calculated at equilibrium and at 34 distinct geometries corresponding to 53 distinct sites for each nucleus. The results were fitted to fourth order in Taylor series expansions and are presented to second order in the coordinates. The carbon-13 shielding is sensitive to all geometrical parameters and displays some unexpected features; most significantly, the shielding at a carbon nucleus ͑C 1 , say͒ is six times more sensitive to change of the C 1 C 2 H 2 angle than it is to change of the H 1 C 1 C 2 angle. In addition, for small changes, ͑C 1 ͒ is more sensitive to the C 2 H 2 bond length than it is to the C 1 H 1 bond length. These, and other, examples of ''unexpected differential sensitivity'' are discussed. The proton shielding surface is much more as expected with ͑H 1 ͒ being most sensitive to the C 1 H 1 bond length, less so to the CC bond length and hardly at all to the C 2 H 2 bond length. The surfaces have been averaged over a very accurate force field to give values of ͑C͒, ͑H͒, and ͑D͒ for the ten isotopomers containing all possible combinations of 12 C, 13 C, 1 H, and 2 H nuclei at 0 K and at a number of selected temperatures in the range accessible to experiment. For the carbon shielding the dominant nuclear motion contribution comes from the bending at ''the other'' carbon atom with the combined stretching contributions being only 20% of those from bending. For the proton shielding it is the stretching of the CH bond containing the proton of interest which provides the major nuclear motion contribution. For ͑C͒ in H 13 C 13 CH at 300 K our best result is 117.59 ppm which is very close to the experimental value of 116.9 ͑Ϯ0.9͒ ppm. For ͑H͒ in H 13 C 13 CH at 300 K we obtain 29.511 ppm which is also in very close agreement with the experimental value of 29.277 ͑Ϯ0.001͒ ppm. Calculated values are also very close to recent, highly accurate carbon and proton isotope shifts in the ten isotopomers; carbon isotope shifts differ by no more than 10% from the measured values and proton isotope shifts are generally in even better agreement than this. The observed anomaly whereby the 13 C isotope shift in H 13 C 12 CD is greater than that in D 13 C 12 CH both with respect to H 13 C 12 CH is explained in terms of the bending contribution at ''the other'' carbon. The observed nonadditivity of deuterium isotope effects on the carbon shielding can be traced to a cross term involving second order bending.

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