CrystalExplorer is a native cross-platform program supported on Windows, MacOS and Linux with the primary function of visualization and investigation of molecular crystal structures, especially through the decorated Hirshfeld surface and its corresponding two-dimensional fingerprint, and through the visualization of void spaces in the crystal via isosurfaces of the promolecule electron density. Over the past decade, significant changes and enhancements have been incorporated into the program, such as the capacity to accurately and quickly calculate and visualize quantitative intermolecular interactions and, perhaps most importantly, the ability to interface with the Gaussian and NWChem programs to calculate quantum-mechanical properties of molecules. The current version, CrystalExplorer21, incorporates these and other changes, and the software can be downloaded and used free of charge for academic research.

We present a new relativistic formulation for the calculation of nuclear magnetic resonance ͑NMR͒ shielding tensors. The formulation makes use of gauge-including atomic orbitals and is based on density functional theory. The relativistic effects are included by making use of the zeroth-order regular approximation. This formulation has been implemented and the 199 Hg NMR shifts of HgMe 2 , HgMeCN, Hg͑CN͒ 2 , HgMeCl, HgMeBr, HgMeI, HgCl 2 , HgBr 2 , and HgI 2 have been calculated using both experimental and optimized geometries. For experimental geometries, good qualitative agreement with experiment is obtained. Quantitatively, the calculated results deviate from experiment on average by 163 ppm, which is approximately 3% of the range of 199 Hg NMR. The experimental effects of an electron donating solvent on the mercury shifts have been reproduced with calculations on HgCl 2 ͑NH 3 ͒ 2 , HgBr 2 ͑NH 3 ͒ 2 , and HgI 2 ͑NH 3 ͒ 2 . In addition, it is shown that the mercury NMR shieldings are sensitive to geometry with changes for HgCl 2 of approximately 50 ppm for each 0.01 Å change in bond length, and 100 ppm for each 10°change in bond angle.

The PI 4 + cation has an extremely large negative 31 P nuclear magnetic resonance chemical shift, due to spin-orbit coupling: A quantum-chemical prediction and its confirmation by solid-state nuclear magnetic resonance spectroscopy Density functional analysis of 13 C and 1 H chemical shifts and bonding in mercurimethanes and organomercury hydrides: The role of scalar relativistic, spin-orbit, and substituent effects A formulation for the calculation of nuclear magnetic resonance ͑NMR͒ shielding tensors, based on density functional theory ͑DFT͒, is presented. Scalar-relativistic and spin-orbit coupling effects are taken into account, and a Fermi-contact term is included in the NMR shielding tensor expression. Gauge-including atomic orbitals ͑GIAO͒ and a frozen-core approximation are used. This formulation has been implemented, and 1 H and 13 C NMR shifts of hydrogen and methyl halides have been calculated and show good agreement with experiment. 13 C NMR shifts of 5d transition metal carbonyls have been calculated and show improved agreement with experiment over previous scalar-relativistic calculations. For the metal carbonyls it is shown explicitly that the combination of spin-orbit coupling and magnetic field mixes spin triplet states into the ground state, inducing a spin density that then interacts with the nuclei of the metal carbonyl via the Fermi-contact term. Results indicate that the Fermi-contact contribution to the 13 C NMR of the metal carbonyl ions increases with increasing oxidation state of the ion. It is reasoned that as the oxidation state increases, back bonding decreases and bonding increases, within the metal-carbon bond, thus facilitating a greater transfer of spin density from the metal to the carbon nucleus, and thus increasing the Fermi-contact contribution to the NMR shielding of the carbon.

ABSTRACT:Recently, analytical second derivatives with respect to nuclear coordinates have been implemented in the Amsterdam density functional (ADF) package. This article presents the detailed formalism of that implementation. Calculations on small molecules such as methane show good agreement between the analytical and numerical frequencies. Calculations on benzene and larger molecules show that the analytical second derivatives code is 2 to 3 times faster than the numerical. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem 104: [645][646][647][648][649][650][651][652][653][654][655][656][657][658][659] 2005 Key words: analytical; derivatives; Hessian; DFT; ADF; second derivatives 1. ADF Package T he second derivatives of the molecular energy with respect to nuclear coordinates are required to calculate the vibrational frequencies of a molecule. They are also required to calculate the Hessian from which stationary points can be characterized as maxima, minima, or saddle points.Recently, analytical second derivatives have been implemented in the Amsterdam density functional package (ADF) [1][2][3]. This article presents the detailed formalism of that implementation.ADF is a package that was initially developed by Baerends and coworkers [4 -7], and further developed over the years by a great many researchers and programmers throughout the world. ADF uses density functional theory (DFT) exclusively and provides a substantial range of exchange-correlation functionals.

In this and a subsequent article, the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. In the given first paper, various issues are explored that are related to this goal. It is shown that both the relativistic DFT-ZORA (zeroth-order regular approximation, as developed for NMR properties by Wolff, S. K.; Ziegler, T.; van Lenthe, E.; Baerends, E. J. J. Chem. Phys. 1999, 110, 7689) and the older quasi-relativistic (QR) DFT methods are applicable to these compounds. Another popular relativistic method, the use of relativistic effective core potentials (ECP) for the calculation of ligand NMR parameters, is tested as well. It is demonstrated that the ECP approach is beyond its limits for the very heavy actinide compounds. Comparing the ZORA and Pauli approaches, it is found that Pauli is more accurate for the 1 H NMR in UF 6-n (OCH 3 ) n compounds whereas ZORA is more accurate in other cases. This is in contrast to earlier studies that always showed ZORA to be superior. The neglect of spin-orbit effects, leading to scalar relativistic approximations, is possible in some cases. In other cases, however, spin-orbit cannot be neglected. For instance in UF 5 (OCH 3 ), a large spin-orbit chemical shift of about 7 ppm has been found for the 1 H nuclei but only small effects for the other ligand nuclei. The large influences of the reference geometry, the reference compound, and the exchange correlation (XC) functional are demonstrated and discussed. The 19 F chemical shift tensor in UF 6 is well reproduced by the ZORA and QR methods. However, for the 19 F chemical shifts in UF 6-n Cl n compounds, only some experimental trends could be reproduced by the calculations. Possible explanations are discussed for these shortcomings, including the choice of model XC functional.