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Using response methods at the RPA level we have calculated mean excitation energies of the 3d-elements and all their cations. We have shown that the dependence of mean excitation energies of the cations on the number of electrons is nearly the same for all 3d-elements. Using a quadratic Z-dependence of mean excitation energies in isoelectronic series, we have estimated mean excitation energies of some of the more highly charged cations of K, Ca, Ga, Ge, As, Se, Br and Kr. Also estimated values for the mean excitation energies of singly, negatively charged ions of 3d-elements are reported. We have shown how to calculate orbital mean excitation energies for the 3datoms from the mean excitation energy of their cations.

A benchmark study of several correlated second-order methods for frequency-dependent polarizabilities has been carried out. For the benchmark, a set of 14 (hetero)aromatic medium-sized molecules has been chosen. For the first time, CC3 polarizabilities are reported for these molecules using Sadlej's polarized triple-ζ basis set, and for a subset of these molecules the polarizabilities were obtained at the CC3 level also with the larger aug-cc-pVTZ basis set. These CC3 values are used as the reference values for benchmarking the second-order methods: SOPPA, SOPPA(CC2), SOPPA(CCSD), CC2, as well as CCSD. The influence of different basis sets, aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-pVQZ, d-aug-cc-pVTZ, and Sadlej's polarized triple-ζ basis set, on static and frequency-dependent polarizabilities was investigated for the full set of molecules at the SOPPA level. It was found that the choice of basis set had a somewhat greater influence on the frequency-dependent polarizabilities than on the static polarizabilities, but all effects were small. The aug-cc-pVTZ basis set performed adequately for both static and frequency-dependent polarizabilities, having an insignificant offset from the values obtained with the larger d-aug-cc-pVTZ and aug-cc-pVQZ basis sets. Comparing the second-order methods, SOPPA, SOPPA(CC2), SOPPA(CCSD), CC2, as well as CCSD, to the CC3 reference values, it was found that the best performing method was CCSD, as expected. The SOPPA method, on the contrary, outperformed the CC2 method, suggesting the use of SOPPA rather than CC2 for polarizabilities, at least for these kinds of molecules. The SOPPA results were found to improve further when the Møller-Plesset correlation coefficients in the wave function were replaced by coupled-cluster amplitudes in the SOPPA(CC2) and SOPPA(CCSD) methods. Finally, a comparison was made for a small subset of the molecules between experimental data and calculated polarizabilities. It shows that, for this set of molecules, the

The second-order non-iterative doubles corrected RPA method (RPA(D)) has been extended to triplet excitation energies and the doubles corrected HRPA method (HRPA(D)) as well as a shifted version (s-HRPA(D)) for calculating singlet and triplet excitation energies are presented here for the first time. A benchmark set consisting of 20 molecules with a total of 117 singlet and 71 triplet excited states has been used to test the performance of the new methods by comparison with previous results obtained with the SOPPA and the CC3 methods. In general, the second-order doubles corrections to RPA and HRPA significantly reduce both the mean deviation as well as the standard deviation of the errors compared to the CC3 results. The new methods approach the accuracy of the SOPPA method while using only 10 - 60% of the calculation time.

This study investigates the performance of two approximations to the popular second order polarization propagator approximation (SOPPA), the doubles-corrected methods RPA(D) and HRPA(D), in calculating carbon-carbon spin-spin coupling constants (SSCCs) in 39 saturated carbocycles, totaling 188 unique coupling constants. RPA(D) scales an order below SOPPA in computational complexity while HRPA(D) differs from SOPPA in the leading coeffcient. These methods may therefore prove benecial in predictions of coupling constants of large molecules. It was found that HRPA(D) performs similarly to SOPPA in terms of accuracy for all coupling constants as well as signicantly improves on RPA(D). With a roughly 55% reduction in computation time from SOPPA to HRPA(D), the latter shows great promise for the calculation of nuclear indirect carbon-carbon SSCCs in saturated carbocycles.

NMR shielding and spin-spin coupling constants of cis and trans isomers of FNNF have been determined to near-quantitative accuracy from ab initio calculations. The FNNF system, containing multiple N-F bonds and fluorine atoms, provides a severe test of computational methods. Coupled-cluster methods were used with large basis sets and complete basis set (CBS) extrapolations of the equilibrium geometry results, with vibrational and relativistic corrections. Shielding constants were calculated with basis sets as large as aug-cc-pCV7Z, together with coupled-cluster expansions up to CCSDT, at the all-electron CCSD(T)/aug-cc-pCVQZ optimized geometries. Spin-spin coupling constants have been determined with specialized versions of the correlation consistent basis sets ccJ-pVXZ, further augmented with diffuse functions. All-electron coupled-cluster methods up to CC3 were applied in these calculations. The results of this work highlight the application of state-of-the-art theoretical techniques, and provide the most accurate NMR properties of FNNF to date, which can serve to guide and supplement NMR experimentation.

The performance of different polarization propagator methods, RPA, RPA(D), HRPA, HRPA(D) and SOPPA have been tested against CC3 values for both static and dynamic polarizabilities. The test set consists of 14 (hetero-)aromatic medium size organic molecules, mostly with a high degree of symmetry. The benchmark of the methods remarkably reveals that RPA and HRPA(D) yield results comparable with the CC3 values and that they outperform SOPPA for these molecules. For a subset of the molecules a comparison could be made to experimental values. The comparison for static polarizabilities proves that RPA and HRPA(D) as well as RPA(D) reproduce experimental values to a satisfying precision, whereas the SOPPA method compared to these two methods appears to perform only adequately. An investigation of the performance of Sadlej’s polarized triple zeta basis set against Dunning’s augcc-pVTZ basis set was also carried out. It is found, that in contrast to other methods, Sadlej’s basis set did not perform sufficiently compared to the larger aug-cc-pVTZ basis set for the RPA based methods.

Assembled together with the most common qubits used in NMR quantum computation experiments, spin--1/2 nuclei, such as 113Cd, 199Hg, 125Te and 77Se could leverage the prospective scalable quantum computer architectures, enabling many and heteronuclear qubits for NMR quantum information processing (QIP) implementations. A computational design strategy for prescreening recently synthesized complexes of cadmium, mercury, tellurium, selenium and phosphorus (called MRE complexes) as suitable qubit molecules for NMR QIP is reported. Chemical shifts and spin--spin coupling constants in five MRE complexes were examined using the spin--orbit zeroth order regular approximation (ZORA) at the density functional theory (DFT) level and the four--component relativistic Dirac-Kohn-Sham approach. In particular the influence of different conformers, basis sets, exchange-correlation functionals and methods to treat the relativistic as well as solvent effects were studied. The differences in the chemical shifts and spin--spin coupling constants between different low energy conformers of the studied complexes were found to be very small. The TZ2P basis set was found to be the optimum choice for the studied chemical shifts, while the TZ2P--J basis set was the best for the couplings studied in this work. The PBE0 exchange-correlation functional exhibited the best performance for the studied MRE complexes. The addition of solvent effects has not improved on the gas phase results in comparison to experiment, with the exception of the phosphorus chemical shift. The use of MRE complexes as qubit molecules for NMR QIP could face the challenges in single qubit control and multiqubit operations. They exhibit chemical shifts appropriately dispersed, allowing qubit addressability and exceptional large spin--spin couplings, which could reduce the time of quantum gate operations and likely preserve the coherence.

We have investigated the relationship between two methods to obtain mean excitation energies of large samples using a modified Bragg rule, one method using Bragg’s rule to determine elemental mean excitation energies from experimental stopping power data, and another method going the opposite way, that is determining compound mean excitation energies from theoretical elemental mean excitation energies and bond correction factors. We show how to obtain bond correction factors from elemental mean excitation energies and vice versa. The comparison leads to insight into the importance of the effect of chemical binding on the experimentally determined elemental mean excitation energies. We also introduce the concept of atomic correction factor that links theoretical, gas phase atomic mean excitation energies to elemental mean excitation energies.

The interfacial tension of systems containing water, n-decane, and model naphthenic acids were investigated using a predictive model based on COSMO-RS theory and experimental pendant drop measurements. Five naphthenic acid homologues that are considered to be representative of surfactants inherent to crude oil were dissolved in n-decane at equal concentrations. The interfacial tensions of the five systems at an acid concentration of 1.66 mol% relative to n-decane were experimentally determined to be 27-30 mN/m. The interfacial tensions of the five different acid-decane phases against water were also predicted using density functional theory (DFT) calculations and COSMO-RS theory. The accuracy of the predictions was very good as confirmed through pendant drop measurements of the interfacial tension. The mean-absolute deviation between experimental and predicted values was 2.6 mN/m thus demonstrating the high predictive power of COSMO-RS theory for calculating the interfacial tension at oil-water interfaces in the presence of surface-active compounds.

A benchmark study of several correlated second-order methods for frequency dependent polarizabilities has been carried out. For the benchmark, a set of 14 (hetero-)aromatic medium sized molecules has been chosen. For the first time CC3 polarizabilities are reported for these molecules using Sadlej's polarized triple-zeta basis set and for a subset of these molecules the polarizabilities were obtained at the CC3 level also with the larger aug-cc-pVTZ basis set. These CC3 values are used as the reference values for benchmarking the second-order methods: SOPPA, SOPPA(CC2), SOPPA(CCSD), CC2 as well as CCSD. The influence of different basis sets: aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-pVQZ, d-aug-cc-pVTZ and Sadlej's polarized triple-zeta basis set, on static and frequency dependent polarizabilities was investigated for the full set of molecules at the SOPPA level. It was found, that the choice of basis set had a somewhat greater influence on the frequency dependent polarizabilities than on the static ones, but all effects were small. The aug-cc-pVTZ basis set performed adequately for both static and frequency dependent polarizabilities, having an insignificant offset from the values obtained with the larger d-aug-cc-pVTZ and aug-cc-pVQZ basis sets. Comparing the second-order methods, SOPPA, SOPPA(CC2), SOPPA(CCSD), CC2 as well as CCSD to the CC3 reference values, it was found that the best performing method was CCSD, as expected. The SOPPA method, on the other hand, outperformed the CC2 method, suggesting the use of SOPPA rather than CC2 for polarizabilities, at least for these kinds of molecules. The SOPPA results were found to improve further, when the Møller-Plesset correlation coefficients in the wavefunction were replaced by coupled cluster amplitudes in the SOPPA(CC2) and SOPPA(CCSD) methods. Finally, a comparison was made for a small subset of the molecules between experimental data and calculated polarizabilities. It shows that, for this set of molecules, the trend in

We report bond correction factors that can be used to calculate molecular mean excitation energies including the effects of chemical bonding. The calculations are based on an extension of Bragg’s rule. We report results for several bonds – neutral and charged - involving gas phase atoms in the first, second and third row of the periodic system. The bond correction factors are dimensionless and turn out to be nearly constant and of the order 1-2. The method is applied to the calculations of mean excitation energies of linear hydrocarbons, amino acids and molecules and molecular ions of astrophysical interest. Examples show that chemical binding effects increase the molecular mean excitation energies with between 4 % to 15 %, smallest for linear, unsaturated molecules and largest for molecules with longer aliphatic chains.

NMR shielding and spin-spin coupling constants of cis and trans isomers of FNNF have been determined to near-quantitative accuracy from ab initio calculations. The FNNF system, containing multiple N-F bonds and fluorine atoms, provides a severe test of computational methods. Coupled-cluster methods were used with large basis sets and complete basis set (CBS) extrapolations of the equilibrium geometry results, with vibrational and relativistic corrections. Shielding constants were calculated with basis sets as large as aug-cc-pCV7Z, together with coupled-cluster expansions up to CCSDT, at the all-electron CCSD(T)/aug-cc-pCVQZ optimized geometries. Spin-spin coupling constants have been determined with specialized versions of the correlation consistent basis sets ccJ-pVXZ, further augmented with diffuse functions. All-electron coupled-cluster methods up to CC3 were applied in these calculations. The results of this work highlight the application of state-of-the-art theoretical techniques, and provide the most accurate NMR properties of FNNF to date, which can serve to guide and supplement NMR experimentation.

The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex molecular environments. The platform is written in Python and defines a means for library communication and interaction. Intermediate data such as integrals are exposed to the platform and made accessible to the user in the form of NumPy arrays, and the resulting data are extracted, analyzed, and visualized. Complex computational protocols that may, for instance, arise due to a need for environment fragmentation and configuration-space sampling of biochemical systems are readily assisted by the platform. The platform is designed to host additional software libraries and will serve as a hub for future modular software development efforts in the distributed Dalton community.

The second‐order noniterative doubles‐corrected random phase approximation (RPA) method has been extended to triplet excitation energies and the doubles‐corrected higher RPA method as well as a shifted version for calculating singlet and triplet excitation energies are presented here for the first time. A benchmark set consisting of 20 molecules with a total of 117 singlet and 71 triplet excited states has been used to test the performance of the new methods by comparison with previous results obtained with the second‐order polarization propagator approximation (SOPPA) and the third order approximate coupled cluster singles, doubles and triples model CC3. In general, the second‐order doubles corrections to RPA and HRPA significantly reduce both the mean deviation as well as the standard deviation of the errors compared to the CC3 results. The accuracy of the new methods approaches the accuracy of the SOPPA method while using only 10–60% of the calculation time