Stationary coupled cluster response: Role of cubic terms in molecular properties

We have demonstrated an application of a stationary coupled cluster response approach for molecular properties using an Euler functional. This involves terms which are of cubic power in cluster amplitudes. We have shown that these are important terms and have also discussed the convergence properties of the functional for higher order properties.     

An open-shell coupled-cluster response method for static properties

This paper deals with a multideterminantal model space-based coupled-cluster response approach suitable for the calculation of static properties of quasi-degenerate systems. The firstorder static property of one-valence-hole/particle system using this approach has been specifically discussed.     

Properties of hydrogen molecular ion with static screened coulomb and exponential cosine screened coulomb potentials

We have investigated the properties of hydrogen molecular ion (H) interacting with screened Coulomb potentials. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine‐screened Coulomb potential. Simulating the localized motion of the nuclei by using high powers of the internuclear coordinate in the generalized Hylleraas‐type wave function we have been able to obtain reasonably accurate binding energies for 1¹S(J = 0, ν = 0) and 2¹S(J = 0, ν = 1) states for various values of the screening parameter within the frame work of Ritz variational method. Borromean bindings are found to exist in the ion for a wide range of the screening parameter. Furthermore, expectation values for various operators and cusp condition have been calculated. Results for the unscreened case are in nice agreement with some of the accurate results available in the literature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A perspective on nonresonant and resonant electronic response theory for time-dependent molecular properties

The development of electronic response theory in quantum chemistry has been reviewed, starting from the early 1970's and reaching the current state-of-the-art. The general theory has been applied to the calculation of a large number of spectroscopic parameters over the years, and it has been implemented for the majority of standard electronic structure methods. Two formulations of response theory, the Ehrenfest expectation value and the quasi-energy derivative formulation, have turned into leading alternatives for the derivation of computationally tractable expressions of response functions, and they are here reviewed with an attempt to, as far as possible, leave out technical details. A set of four steps are identified as common in derivations of response functions, and the two formulations are compared along this series of steps. Particular emphasis is given to the situation when the oscillation of the weak external electromagnetic field is in resonance with a transition frequency of the system. The formation of physically sound response functions in resonance regions of the spectrum is discussed in light of the causality condition and the Kramers-Kronig relations, and it is achieved in wave function theory by means of the introduction of relaxation parameters in a manner that mimics what one sees in density matrix theory. As a working example, equations are illustrated by their application to a two-state model for para-nitroaniline including the ground and the lowest charge-transfer state in the electric dipole approximation.     

Efficient polarized basis sets for evaluation of static and dynamic molecular electric properties

New medium size Gaussian‐type basis set R‐ORP for evaluation of static and dynamic electric properties in molecular systems is presented. It is obtained in a close resemblance to the original ORP basis set, from the source basis set through addition of two first‐order polarization functions whose exponent values are optimized with respect to the finite field restricted open‐shell Hartree–Fock (ROHF) atomic polarizabilities. As the source set the VTZ basis set of Ahlrichs and coworkers, augmented with additional diffuse functions and contracted to the form [6s/3s] for hydrogen and [11s7p/4s3p] for carbon through fluorine, is chosen. The resulting basis set is of the form [6s2p/3s2p] for hydrogen and [11s7p2d/4s3p2d] for other atoms. Presented basis set is next tested in the CCSD static and dynamic molecular polarizability and hyperpolarizability calculations for a set of ten and four test molecules, respectively, for which very accurate reference data exist. Additionally, the recently developed ORP basis set is employed in the calculations to examine the limits of its applicability. Results are compared to the literature data obtained in both, large and diffuse, as well as reduced‐size basis sets. In the case of polarizability calculations, the aug‐pc‐1 and R‐ORP are the optimal choices among the investigated smaller basis sets, with the overall performance of the aug‐pc‐1 set being better. Among the larger sets, the ORP performs better in the case of average polarizability, while the RMSE values for polarizability anisotropy are practically identical for d‐aug‐cc‐pVDZ and ORP sets. Finally, the R‐ORP and ORP basis sets compete other small bases in the evaluation of the first hyperpolarizability in investigated systems. © 2016 Wiley Periodicals, Inc.     

An efficient, fragment-based electronic structure method for molecular systems: self-consistent polarization with perturbative two-body exchange and dispersion

We report a fragment-based electronic structure method, intended for the study of clusters and molecular liquids, that incorporates electronic polarization (induction) in a self-consistent fashion but treats intermolecular exchange and dispersion interactions perturbatively, as post-self-consistent field corrections, using a form of pairwise symmetry-adapted perturbation theory. The computational cost of the method scales quadratically as a function of the number of fragments (monomers), but could be made to scale linearly by exploiting distance-dependent thresholds. Extensive benchmark calculations are reported using the S22 database of high-level ab initio binding energies for dimers, and we find that average errors can be reduced to <1 kcal/mol with a suitable choice of basis set. Comparison to ab initio benchmarks for water clusters as large as (H(2)O)(20) demonstrates that the method recovers ?90% of the binding energy in these systems, at a tiny fraction of the computational cost. As such, this approach represents a promising path toward accurate, systematically improvable, and parameter-free simulation of molecular liquids.     

Multiconfigurational second-order perturbative methods: Overview and comparison of basic properties

Summary The multiconfigurational second-order perturbative treatments of molecular electronic calculations can be classified into four groups: i) quasi-degenerate perturbation theory (QDPT) in the basis of determinants, ii) non-degenerate perturbation theory applied to eigenvectors resulting from a truncated CI, ii) QDPT in a model space of non-interacting multiconfigurational functions, iv) intermediate Hamiltonians theory, and examined according to three criteria: i) risk of numerical instability due to intruder states, ii) ability to treat the effect of the outer-space on the model space component of the wavefunction, especially important for the treatment of weakly avoided crossings, iii) separability for (A* ... B) problems. None of the existing methods satisfies these three criteria, as shown both by model analysis and real ab initio calculations on LiF and CuF.     

Regularization method and molecular integrals with singular exponential functions

The regularization principle, which is based on the concept of linearly independent singular functions, makes it possible to calculate many important types of molecular matrix elements arising in the variational LCAO-MO-SCF scheme. This is done using a direct approach that employs reduction of these elements to finite sums of convergent and divergent one-electron integrals. A universal algorithm is developed to calculate two-center one-electron molecular integrals involving both singular and ordinary Slater functions. The numerical stability of the algorithms and the accuracy of the integral calculation are analyzed, and numerical estimates are given. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Struktunoi Khimii, Vol. 35, No. 2, pp. 3–11, March–April, 1994. Translated by L. Chernomorskaya     

Stationary Phases 21: A New Polar Substituted Triazine Stationary Phase for HPLC

A method for preparing a new polar substituted triazine stationary phase is described. The structure of the triazine phase on silica was characterized by elemental analysis, and by FTIR, solid state FT-¹³C NMR, and ²⁹Si NMR spectral analysis. The chromatographic properties of this packing material have been evaluated by using a number of different solutes, and the properties compared with those of a commercial stationary phase RP-18. It is found that this triazine phase has weak π-donor ligands on the silica surface.     

Structural and static electric response properties of highly symmetric lithiated silicon cages: Theoretical predictions

It is shown by density functional theory calculations that high symmetry silicon cages can be designed by coating with Li atoms. The resulting highly symmetric lithiated silicon cages (up to D_5d symmetry) are low‐lying true minima of the energy hypersurface with binding energies of the order of 4.6 eV per Si atom and moderate highest occupied molecular orbital–lowest unoccupied molecular orbital gaps. Moreover, relying on a systematic study of the electric response properties obtained by ab initio (Hartree–Fock, MP2, and configuration interaction singles (CIS)) and density functional (B3LYP, B2PLYP, and CAM‐B3LYP) methods, it is shown that lithium coating has a large impact on the magnitude of their second hyperpolarizabilities resulting to highly hyperpolarizable species. Such hyperpolarizable character is directly connected to the increase in the density of the low‐lying excited states triggered by the interaction between the Si cage and the surrounding Li atoms. © 2012 Wiley Periodicals, Inc.     

Development of a sum-over-states density functional theory for both electric and magnetic static response properties

It is shown that it is possible to formulate a sum-over-states (SOS) response theory for static perturbations based directly on the Kohn-Sham formulation of density functional theory (DFT). The SOS-DFT response theory affords expressions analogous to those obtained from the classical Raleigh-Schrodinger perturbation theory, where use is made of a complete set of ground and excited state energies and wave functions. The static SOS-DFT response theory is applicable for both real and imaginary perturbations. The theory is established by making use of time-dependent DFT taken to zero frequency with the use of the adiabatic approximation. In the SOS-DFT formulation the expression for electric (e.g., polarization) and magnetic (e.g., magnetization) response properties are symmetrical.     

Stationary phases with special structural properties for high-throughput separation techniques: preparation, characterization and applications

Stationary phases with specific structural properties for high-throughput liquid chromatographic (LC) techniques are described. Special attention was paid to phases with special structural properties, mainly containing internal functional group (e.g. amide). Such materials are generally called "embedded phases". There are phases created in amidation process of aminopropylated silica gel, especially phases based on biological compounds, like phospholipids and cholesterol, which are called immobilized artificial membranes (IAM's). The synthesis and applications of polar embedded amide LC stationary phases were also reviewed. Methods of characterization of synthesized packing materials were presented, with general focusing on spectroscopic measurements like (13C and 29Si CP/MAS NMR and FT-IR), elemental and thermal analysis as well as chromatographic quantitative structure-retention relationships (QSRR) and extended chemometric tests. The potential applications of various dedicated stationary phases in a high-throughput LC screening procedures were also presented.     

Using molecular quantum similarity measures under stochastic transformation to describe physical properties of molecular systems

The application of molecular quantum similarity measures (MQSM) to correlate physicochemical properties is reported. Satisfactory quantitative structure-property relationship (QSPR) models are obtained for three molecular sets, where boiling points and chromatographic retention times and indices are studied. In this work, MQSM are scaled using a stochastic transformation and related to molecular properties using the partial least-squares technique.     

On the molecular interpretation of the static dielectric properties of nematic liquid crystals

This paper shows that on the basis of the temperature dependence of the principal static permittivities of nematics epsilon (T) and epsilon (T), using the Maier-Meier equations, the following quantities can be obtained: (i) the angle between the dipole moment vector and the long axis of the mesogenic molecules, (ii) the square of the apparent molecular dipole moment mu2app(T) and (iii) the nematic order parameter S(T).     

A software package for the generation of noise with widely divergent spectral properties : The Simulation of Realistic Stationary Detector Noise

The computer program discussed is capable of generating stationary noise with optional statistical parameters. Five standard noise types can be generated: white, 1/f, first order, Gaussian, and damped cosine noise. The input to the program can be a measured or arbitrarily chosen autocovariance function (or power spectrum). The autocovariance function (power spectrum) computed from the generated noise will be in perfect agreement with the input autocovariance function, if an infinite number of noise data is generated. Some theoretical work on noise generation on the basis of the autocovariance function is described. The autocovariance function of 1/f noise is theoretically derived from the power spectrum, based on a model described earlier. A few examples of the use of the program and an example of a possible application are given. A peak-finding procedure is tested with a simulated chromatogram contaminated with different types of noise. Applications are possible in data processing, information extraction, simulation and automation.     

A variational method to calculate static electronic properties

Using a coupled cluster form of the wave function, a variational method is formulated for calculation of static properties of any order. Corresponding to an appropriate perturbed hamiltonian H() including the relevant static property, a size consistent functional is set up. In a hierarchical fashion, properties of different orders may be found out using a variational method.     

Changes in molecular properties with changes in molecular geometry: A partitioning into electronic and nuclear components

Most one-electron properties vary with changes in molecular conformation. Although the nuclear component remains constant for some of the one-electron property changes and thus the overall change depends only on the electronic change this result is not general. Often the change in the nuclear component dominates the overall change in a molecular property. An analysis of the changes in a number of one-electron properties with changes in molecular geometry in terms of the changes in the nuclear and the electronic components is presented. The inversion of ammonia and the torsion of ethane were chosen as important examples of conformational changes and the changes in molecular one-electron properties studied.     

A method for correlations analysis of coordinates: applications for molecular conformations

We describe a new method to analyze multiple correlations between subsets of coordinates that represent a sample. The correlation is established only between specific regions of interest at the coordinates. First, the region(s) of interest are selected at each molecular coordinate. Next, a correlation matrix is constructed for the selected regions. The matrix is subject to further analysis, illuminating the multidimensional structural characteristics that exist in the conformational space. The method's abilities are demonstrated in several examples: it is used to analyze the conformational space of complex molecules, it is successfully applied to compare related conformational spaces, and it is used to analyze a diverse set of protein folding trajectories.