The calculation of C13 chemical shielding tensors in ionic compounds utilizing point charge arrays obtained from Ewald lattice sums

Abstract

An embedded ion method is proposed for accurately calculating the C13 chemical shift tensors in ionic compounds. The method models an ionic crystal by embedding an ion of interest inside an array of point charges. The potential, produced by an infinite ionic lattice, at the location of the ion of interest can be simulated accurately utilizing a point charge array obtained by the Ewald summation method. The Ewald summation method, as implemented in the computer program EWALD, in conjunction with the quantum-mechanics program GAUSSIAN 98 is used to generate a self-consistent point charge array that simulates the Ewald potential in a defined region at the center of the array. Subsequently, the chemical shift tensor calculation is performed using GAUSSIAN 98 on the ion of interest positioned in the region inside the point charge array in which the Ewald potential is established. The embedded ion method was tested on potassium methyl-trithiocarbonate (KS2CSCH3) whose crystal lattice is composed of potassium cations and molecular S2CSCH3− anions. The principal values of the C13 chemical shift tensors in KS2CSCH3 were measured in a stationary cross polarization nuclear magnetic resonance experiment. It is shown that the correlation between experimental and calculated principal values improves significantly when the C–H bond distances are optimized from their x-ray values. It is further demonstrated that a substantial improvement in the correlation is obtained when the chemical shielding tensor calculation is performed on an S2CSCH3− anion embedded inside a point charge array obtained by the Ewald summation method. The embedded ion method was completed applying the B3P86/cc-pVTZ, B3LYP/cc-pVTZ, and MP2/cc-pVDZ quantum-mechanical computations and the various results are compared and analyzed.

Modeling solid-state effects on NMR chemical shifts using electrostatic models

“…The procedure in the calculations established by Stueber et al 11 is first to obtain the partial atomic charges from a calculation of an isolated molecule or ion. The method chosen to calculate these partial charges was the natural bond orbital (NBO), 33 as implemented in the Gaussian suite of programs.…”

“…18,19 A variety of point charge methods have been used to reproduce successfully the solidstate effects observed on both 13 C and 15 N chemical shifts, 3 -12 but as these calculations were done with dissimilar sets of compounds and using diverse computational approaches it is difficult to decide on their relative merits. Among the different point charge methods described in the literature, in this paper we consider the embedded ion method (EIM) 11 and the surface charge representation of the electrostatic embedding potential (SCREEP) 10 methods that have been developed independently in our laboratories. The EIM has been shown to improve the agreement between experimental and calculated chemical shifts in a wide variety of systems, ranging from ionic systems such as potassium carbonate and thiocarbonate 20 to systems with hydrogen bonding 12,21,22 and neutral systems with intermolecular Coulombic interactions such asˇ-HMX.…”

High sensitivity of O17 NMR to p-d hybridization in transition metal perovskites: First principles calculations of large anisotropic chemical shielding

“…Linear response methods have long been used to calculateσ for isolated molecules and clusters. 7,8,9,10,11,12,13 In extended systems complications arise due to the use of periodic boundary conditions (PBC), 14,15,16 and implementations have been limited to planewave-based methods. Recently, an alternative to the linear response method has been proposed based on calculations of the orbital magnetization.…”

Structural investigation of aluminium doped ZnO nanoparticles by solid-state NMR spectroscopy

“…the electric field gradient tensor (EFG, q) and the absolute magnetic shielding tensor s. To this end we made use of the Extended Embedded Ion Method (EEIM), 64 an embedded cluster approach derived from the Embedded Ion Method (EIM), 65,66 whose basic feature is the embedding of the quantum cluster (QC) in a self-consistent point charge field that simulates the environment of an ideal crystal in the electrostatic approximation, which is well suited to the treatment of doped materials at low doping levels. 48 Because the EFG as well as the chemical shift is a local quantity, 67 embedded cluster methods are also suitable for its calculation.…”