Quelling the Geometry Factor Effect in Quantum Chemical Calculations of C NMR Chemical Shifts with the Aid of the pecG- ( = 1, 2) Basis Sets.

A root factor for the accuracy of all quantum chemical calculations of nuclear magnetic resonance (NMR) chemical shifts is the quality of the molecular equilibrium geometry used. In turn, this quality depends largely on the basis set employed at the geometry optimization stage. This parameter represents the main subject of the present study, which is a continuation of our recent work, where new pecG- ( = 1, 2) basis sets for the geometry optimization were introduced.

Getaway from the Geometry Factor Error in the Molecular Property Calculations: Efficient pecG- ( = 1, 2) Basis Sets for the Geometry Optimization of Molecules Containing Light p Elements.

The basis of all molecular property quantum chemical calculations is the correct equilibrium geometry. In this paper, new efficient pecG- ( = 1, 2) basis sets for the geometry optimization of molecules containing hydrogen and p elements of 2-3 periods are proposed. These basis sets were optimized via the property-energy consistent (PEC) algorithm directed to the minimization of the molecular energy gradient relative to the bond lengths.

On the Efficiency of the Density Functional Theory (DFT)-Based Computational Protocol for H and C Nuclear Magnetic Resonance (NMR) Chemical Shifts of Natural Products: Studying the Accuracy of the pecS- ( = 1, 2) Basis Sets.

The basis set issue has always been one of the most important factors of accuracy in the quantum chemical calculations of NMR chemical shifts. In a previous paper, we developed new pecS- ( = 1, 2) basis sets purposed for the calculations of the NMR chemical shifts of the nuclei of the most popular NMR-active isotopes of 1-2 row elements and successfully approbated these on the DFT calculations of chemical shifts in a limited series of small molecules. In this paper, we demonstrate the performance of the pecS- ( = 1, 2) basis sets on the calculations of as much as 713 H and 767 C chemical shifts of 23 biologically active natural products with complicated stereochemical structures, carried out using the GIAO-DFT(PBE0) approach.

New efficient pecS- ( = 1, 2) basis sets for quantum chemical calculations of P NMR chemical shifts.

The basis sets that are used in the quantum chemical calculations of P NMR chemical shifts have always been one of the most important factors of accuracy. Regardless of what high-quality approach is employed, using basis sets of insufficient flexibility in the important angular regions may give poor results and lead to misassignments of the signals in the P NMR spectra. In this work, it was found that the existing nonrelativistic basis sets for phosphorus atom of double- and triple- quality, specialized for the P NMR chemical shifts calculations, are essentially undersaturated in the -angular space that occurred to play a significant role in the overall accuracy of these calculations.

New pecJ- ( = 1, 2) Basis Sets for Selenium Atom Purposed for the Calculations of NMR Spin-Spin Coupling Constants Involving Selenium.

We present new compact pecJ- ( = 1, 2) basis sets for the selenium atom developed for the quantum-chemical calculations of NMR spin-spin coupling constants (SSCCs) involving selenium nuclei. These basis sets were obtained at the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes (SOPPA(CCSD)) level with the property-energy consistent (PEC) method, which was introduced in our previous papers. The existing SSCC-oriented selenium basis sets are rather large in size, while the PEC method gives more compact basis sets that are capable of providing accuracy comparable to that reached using the property-oriented basis sets of larger sizes generated with a standard even-tempered technique.

On the Utmost Importance of the Basis Set Choice for the Calculations of the Relativistic Corrections to NMR Shielding Constants.

The investigation of the sensitivity of the relativistic corrections to the NMR shielding constants (σ) to the configuration of angular spaces of the basis sets used on the atoms of interest was carried out within the four-component density functional theory (DFT). Both types of relativistic effects were considered, namely the so-called heavy atom on light atom and heavy atom on heavy atom effects, though the main attention was paid to the former. As a main result, it was found that the dependence of the relativistic corrections to σ of light nuclei (exemplified here by H and C) located in close vicinity to a heavy atom (exemplified here by In, Sn, Sb, Te, and I) on the basis set used on the light spectator atom was very much in common with that of the Fermi-contact contribution to the corresponding nonrelativistic spin-spin coupling constant ().

New pecJ- ( = 1, 2) Basis Sets for High-Quality Calculations of Indirect Nuclear Spin-Spin Coupling Constants Involving P and Si: The Advanced PEC Method.

In this paper, we presented new -oriented basis sets, pecJ- ( = 1, 2), for phosphorus and silicon, purposed for the high-quality correlated calculations of the NMR spin-spin coupling constants involving these nuclei. The pecJ- basis sets were generated using the modified version of the property-energy consistent (PEC) method, which was introduced in our earlier paper. The modifications applied to the original PEC procedure increased the overall accuracy and robustness of the generated basis sets in relation to the diversity of electronic systems.

New pecS-n (n = 1, 2) basis sets for quantum chemical calculations of the NMR chemical shifts of H, C, N, and O nuclei.

This paper demonstrates the performance of our previously suggested property-energy consistent method on the example of the generation of effective basis sets, pecS-1 and pecS-2, suited for the calculation of hydrogen, carbon, nitrogen, and oxygen chemical shifts. The new basis sets were successfully approbated in the GIAO-DFT calculations of the chemical shifts of 35 molecules using six different functionals. The pecS-1 basis set demonstrated very good accuracy, which makes this small basis set an effective means for the large-scale computations.

Computational Hg NMR.

Theoretical background and fundamental results dealing with the computation of mercury chemical shifts and spin-spin coupling constants are reviewed with a special emphasis on their stereochemical behavior and applications.

Fluorine spin-spin coupling constants of pentafluorobenzene revisited at the ab initio correlated levels.

All possible spin-spin coupling constants, F- F, F- C, and F- H, of pentafluorobenzene were calculated at five different levels of theory, HF, DFT, SOPPA (CCSD), CCSD, and the SOPPA (CCSD)-based composite scheme with taking into account solvent, vibrational, relativistic, and correlation corrections. Most corrections were next to negligible for the long-range couplings but quite essential for the one-bond carbon-fluorine coupling constants. Hartree-Fock calculations were found to be entirely unreliable, while DFT results were comparable in accuracy with the data obtained using the wave function-based methods.

An efficient method for generating property-energy consistent basis sets. New pecJ- ( = 1, 2) basis sets for high-quality calculations of indirect nuclear spin-spin coupling constants involving H, C, N, and F nuclei.

This paper presents a new method of generating property-energy consistent (PEC) basis sets that can be applied to any arbitrary molecular property. The PEC method generates a basis set that is optimized for the molecular property under interest, providing the least possible total molecular energy. The main algorithm of the PEC approach involves Monte Carlo simulations to generate random exponents in the predetermined range.

Efficient J-oriented tin basis sets for the correlated calculations of indirect nuclear spin-spin coupling constants.

New J-oriented tin basis sets, acvXz-J (X = 2, 3, 4), have been developed at the level of the second-order polarization propagator approximation with the coupled-cluster single and double amplitudes, SOPPA (CCSD), for the purpose of correlated calculations of indirect nuclear spin-spin coupling constants involving tin nucleus. High-quality coupled-cluster calculations of several tin-proton and tin-carbon spin-spin coupling constants, performed with one of the newly developed basis sets, namely, the acv3z-J, taking into account relativistic, solvent, and vibrational corrections showed that the acv3z-J basis set is capable to provide reliable results, as compared with the experimental data.

Quantum chemical calculations of Se and Te nuclear magnetic resonance spectral parameters and their structural applications.

An accurate quantum chemical (QC) modeling of Se and Te nuclear magnetic resonance (NMR) spectra is deeply involved in the NMR structural assignment for selenium and tellurium compounds that are of utmost importance both in organic and inorganic chemistry nowadays due to their huge application potential in many fields, like biology, medicine, and metallurgy. The main interest of this review is focused on the progress in QC computations of Se and Te NMR chemical shifts and indirect spin-spin coupling constants involving these nuclei. Different computational methodologies that have been used to simulate the NMR spectra of selenium and tellurium compounds since the middle of the 1990s are discussed with a strong emphasis on their accuracy.

A New Basis Set for the Calculation of C NMR Chemical Shifts within a Non-empirical Correlated Framework.

A new basis set of triple-ζ quality for carbon, 3z-S, is developed and tested at the DFT, MP2, and CCSD(T) levels, taking into account solvent and vibrational corrections for a number of molecules ranging from the smallest fluoromethane, CHF, to the largest 5,10,15,20-tetraphenylporphyrin, CHN. The proposed highly economical 3z-S basis set has been proven to provide very good accuracy in all examinations, comparable to that of the NMR-oriented Jensen's pcS-2 basis set, which is about 50% larger than 3z-S.

Correlated ab initio calculations of one-bond P Se and P Te spin-spin coupling constants in a series of PSe and PTe systems accounting for relativistic effects (part 2).

Synthetic chalcogen-phosphorus chemistry permanently makes new challenges to computational Nuclear Magnetic Resonance (NMR) spectroscopy, which has proven to be a powerful tool of structural analysis of chalcogen-phosphorus compounds. This paper reports on the calculations of one-bond P Se and P Te NMR spin-spin coupling constants (SSCCs) in the series of phosphine selenides and tellurides. The applicability of the combined computational approach to the one-bond P Se and P Te SSCCs, incorporating the composite nonrelativistic scheme, built of high-accuracy correlated SOPPA (CC2) and Coupled Cluster Single and Double (CCSD) methods and the Density Functional Theory (DFT) relativistic corrections (four-component level), was examined against the experiment and another scheme based on the four-component relativistic DFT method.

Hierarchical Basis Sets for the Calculation of Nuclear Magnetic Resonance Spin-Spin Coupling Constants Involving Either Selenium or Tellurium Nuclei.

New basis sets, acvXz-J (X = 2, 3, 4), were designed for tellurium and selenium atoms for the calculation of indirect nuclear spin-spin coupling constants involving selenium or tellurium nuclei. Saturation of angular spaces was performed in an even-tempered manner till achieving the convergence of spin-spin coupling constants under consideration. The high-accuracy correlated SOPPA(CCSD) method was employed in this procedure.

Stereochemical Dependences of P-C Spin-Spin Coupling Constants of Heterocyclic Phosphines.

Phosphorus-carbon spin-spin coupling constants in a series of salient heterocyclic phosphines were calculated at the SOPPA(MP2) level including evaluation of relativistic and solvent effects. A number of the locally dense basis set schemes were thoroughly investigated in terms of their accuracy versus computational demands. The most effective computational scheme was tested in a benchmark series to provide a very good correlation between calculated at the SOPPA(MP2) level and experiment.

On the heavy atom on light atom relativistic effect in the NMR shielding constants of phosphine tellurides.

The relativistic HALA effect has been shown to depend on the spatial deformation of the lone electron pairs of a heavy atom, as demonstrated for alkyl and alkene phosphine tellurides. It was found that HALA effect on phosphorous nuclear magnetic resonance shielding constant is strongly dependent on the spatial arrangements of light substituents on phosphorus, resulting in the deformation of the lone electron pairs of tellurium.

Calculation of Te NMR Chemical Shifts at the Full Four-Component Relativistic Level with Taking into Account Solvent and Vibrational Corrections: A Gateway to Better Agreement with Experiment.

Four-component relativistic calculations of Te NMR chemical shifts were performed in the series of 13 organotellurium compounds, potential precursors of the biologically active species, at the density functional theory level under the nonrelativistic and four-component fully relativistic conditions using locally dense basis set scheme derived from relativistic Dyall's basis sets. The relativistic effects in tellurium chemical shifts were found to be of as much as 20-25% of the total calculated values. The vibrational and solvent corrections to Te NMR chemical shifts are about, accordingly, 6 and 8% of their total values.