A quantum-chemical study on the consequences of geometric modification and chelation on the electronic structure and optical properties of a tetra(carboxylic acid)phenyleneethynylene dye, of interest for chemical sensing applications, is presented. Rotation within the central biphenylene and complexation with divalent metal ions--in particular Cu2+--lead to notable changes in the absorption and...

It is typically assumed that once a Hartree-Fock (HF) reference wave function is determined, the correlated wave function obtained from that HF wave function describes the same electronic state. In this paper, we report the appearance of multiple CCSD solutions obtained from the UHF reference wave function for the known ground state of a chemically interesting molecule, NiH. To determine a corr...

We have performed relativistic many-body calculations of the hyperfine interaction in the 6s and 7s states of Cs, including the off-diagonal matrix element. The calculations were used to determine the accuracy of the semi-empirical formula for the electromagnetic transition amplitude 6s|M 1|7s induced by the hyperfine interaction. We have found that even though the contribution of the many-body...

Computational studies on three tautomeric forms of four 1,5,6,7-tetrahydro- 4H-indazol-4-one derivatives: 1,5,6,7-tetrahydro-4H-indazol-4-one (1), 6,6-dimethyl- 1,5,6,7-tetrahydro-4H-indazol-4-one (2), 3-methyl-1,5,6,7-tetrahydro-4H-indazol-4-one (3) and 3,6,6-trimethyl-1,5,6,7-tetrahydro-4H-indazol-4-one (4), have been performed at different levels, ranging from semiempirical AM1, ab initio Ha...

A new module interfaced to the XD programming package has been used in the evaluation of intermolecular interactions and lattice energies of the crystals of p-nitroaniline, L-asparagine monohydrate and the pentapeptide Boc-Gln-D-Iva-Hyp-Ala-Phol (Boc = butoxycarbonyl, Iva = isovaline = ethylalanine, Phol = phenylalaninol). The electrostatic interactions are evaluated with the atom-centered dist...

We provide accurate assessments of the consequences of violations of self-consistency in HartreeFock (HF) based random phase approximation (RPA) calculations of the centroid energy Ecen of isoscalar and isovector giant resonances of multi-polarities L = 0 − 3 in a wide range of nuclei. This is done by carrying out highly accurate HF-RPA calculations neglecting the particle-hole (ph) spin-orbit ...

The Unitary Correlation Operator Method (UCOM) provides a powerful scheme for carrying out ab initio nuclear structure calculations [1, 2, 3, 4]. In particular, it makes it possible to combine numerically affordable manybody Hilbert spaces with modern realistic NN interactions. Short-range correlations are explicitly taken into account. First results ranging from no-core shell model to HartreeF...

The kinetics of reaction between 4-methylaniline (1), dimethyl acetylenedicarboxylate (2) and formaldehyde (4) has been theoretically investigated to gain further insight into the reaction mechanism. The results of theoretical calculations were achieved using the ab initio method at the HF/6-311g (d, p) level of theory in gas phase. The mechanism of this reaction had 5 steps. Theoretical kineti...

The heats of formation of haloacetylenes are evaluated using the recent W1 and W2 ab initio computational thermochemistry methods. These calculations involve CCSD and CCSD(T) coupled cluster methods, basis sets of up to spdfgh quality, extrapolations to the one-particle basis set limit, and contributions of inner-shell correlation, scalar relativistic effects, and (where relevant) first-order s...