The relatively small diffuse function-augmented basis set, 3-21+G, is shown to describe anion geometries and proton affinities adequately. The diffuse sp orbital exponents are recommended for general use to augment larger basis sets.

Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F

Halogen bonding refers to the non-covalent interactions of halogen atoms X in some molecules, RX, with negative sites on others. It can be explained by the presence of a region of positive electrostatic potential, the sigma-hole, on the outermost portion of the halogen's surface, centered on the R-X axis. We have carried out a natural bond order B3LYP analysis of the molecules CF(3)X, with X = F, Cl, Br and I. It shows that the Cl, Br and I atoms in these molecules closely approximate the [Formula: see text] configuration, where the z-axis is along the R-X bond. The three unshared pairs of electrons produce a belt of negative electrostatic potential around the central part of X, leaving the outermost region positive, the sigma-hole. This is not found in the case of fluorine, for which the combination of its high electronegativity plus significant sp-hybridization causes an influx of electronic charge that neutralizes the sigma-hole. These factors become progressively less important in proceeding to Cl, Br and I, and their effects are also counteracted by the presence of electron-withdrawing substituents in the remainder of the molecule. Thus a sigma-hole is observed for the Cl in CF(3)Cl, but not in CH(3)Cl.

Halogen bonding: the σ-hole

A new implementation of analytical gradients for the polarizable continuum model is presented, which allows Hartree‐Fock and density functional calculations taking into account both electrostatic and nonelectrostatic contributions to energies and gradients for closed and open shell systems. Simplified procedures neglecting the derivatives of the cavity surface and/or using single spheres for XHn groups have also been implemented and tested. The solvent‐induced geometry relaxation has been studied for a number of representative systems in order to test the efficiency of the procedure and to investigate the role of different contributions. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 404–417, 1998

Geometry optimization of molecular structures in solution by the polarizable continuum model

A general procedure is developed for the computation of the total energies of molecules at their equilibrium geometries. Ab initio molecular orbital theory is used to calculate electronic energies by a composite method, utilizing large basis sets (including diffuse‐sp, double‐d and f‐polarization functions) and treating electron correlation by Mo/ller–Plesset perturbation theory and by quadratic configuration interaction. The theory is also used to compute zero‐point vibrational energy corrections. Total atomization energies for a set of 31 molecules are found to agree with experimental thermochemical data to an accuracy greater than 2 kcal mol−1 in most cases. Similar agreement is achieved for ionization energies, electron and proton affinities. Residual errors are assessed for the total energies of neutral atoms.

Gaussian‐1 theory: A general procedure for prediction of molecular energies

Jaguar is an ab initio quantum chemical program that specializes in fast electronic structure predictions for molecular systems of medium and large size. Jaguar focuses on computational methods with reasonable computational scaling with the size of the system, such as density functional theory (DFT) and local second-order Moller–Plesset perturbation theory. The favorable scaling of the methods and the high efficiency of the program make it possible to conduct routine computations involving several thousand molecular orbitals. This performance is achieved through a utilization of the pseudospectral approximation and several levels of parallelization. The speed advantages are beneficial for applying Jaguar in biomolecular computational modeling. Additionally, owing to its superior wave function guess for transition-metal-containing systems, Jaguar finds applications in inorganic and bioinorganic chemistry. The emphasis on larger systems and transition metal elements paves the way toward developing Jaguar for its use in materials science modeling. The article describes the historical and new features of Jaguar, such as improved parallelization of many modules, innovations in ab initio pKa prediction, and new semiempirical corrections for nondynamic correlation errors in DFT. Jaguar applications in drug discovery, materials science, force field parameterization, and other areas of computational research are reviewed. Timing benchmarks and other results obtained from the most recent Jaguar code are provided. The article concludes with a discussion of challenges and directions for future development of the program. © 2013 Wiley Periodicals, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/qua.24481

Jaguar: A high-performance quantum chemistry software program with strengths in life and materials sciences

Calculs ab initio sur les composes MCH 2 X avec M=Li ou Na et X=CH 3 , NH 2 , OH, F, SiH 3 , PH 2 , SH ou Cl, avec corrections de correlation electronique. Comparaison avec especes anioniques correspondantes

Structures and stabilities of α-hetero-substituted organolithium and organosodium compounds. Energetic unimportance of d-orbital effects

The entire set of methyl anions, XCH 2 - , substituted by first-row substituents, Li, BeH, BH 2 , CH 3 , NH 2 , OH, and F, was examined at various ab initio levels. Diffuse orbital-augmented basis sets, such as 4-31+G and 6-31+G ∗ , are needed to describe the energies of these anions adequately. Estimates of proton affinities are further improved by second-order Moller-Plesset (MP2) electron correlation corrections, but relative energies are less affected. The methyl group in the ethyl anion is destabilizing, the amino substituent is borderline, but all other groups are stabilizing. Very large π effects are exhibited by BH 2 and BeH groups; inductive stabilization by the electronegative F and OH groups is less effective. Lithium also is stabilizing, but the best singlet geometry of CH 2 Li - is not planar. A planar CH 2 Li - triplet with a π 1 configuration may be lower in energy.

Stabilization of methyl anions by first‐row substituents. The superiority of diffuse function‐augmented basis sets for anion calculations

The energetic effects of the addition of diffuse functions to molecules with second-row elements are much less dramatic than those for their first-row counterparts. Although diffuse functions on second-row elements have little effect on the geometries and vibrational frequencies of neutral molecules, significant changes are found for anions. While the largest basis set, 6-31 + G*, generally performs best, the results at 3-21 + G* are comparable, and this basis can be recommended for practical applications.

An evaluation of the performance of diffuse function‐augmented basis sets for second row elements, Na‐Cl

Calculs MO ab initio (4-31 G) sur les cyclopropanes C 3 H 5 X et les composes isopropyliques C 3 H 7 X avec X=Li, BeH, BH 2 , CH 3 , NH 2 , OH, F: le groupe cyclopropyle est plus electronegatif que le groupe isopropyle. Discussion en termes d'interactions d'orbitales

Günther W. Spitznagel

Papers

Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F

Structures and stabilities of α-hetero-substituted organolithium and organosodium compounds. Energetic unimportance of d-orbital effects

Stabilization of methyl anions by first‐row substituents. The superiority of diffuse function‐augmented basis sets for anion calculations

An evaluation of the performance of diffuse function‐augmented basis sets for second row elements, Na‐Cl

Substituent effects on the geometries and energies of cyclopropanes and the corresponding 2-propyl derivatives