0000000000075727
AUTHOR
A. Sánchez De Merás
Low-lying Rydberg states of HCl.
Vertical excitation energies belonging to some different Rydberg series of hydrogen chloride have been determined with a coupled-cluster theoretical approach. These excitation energies have allowed us to calculate electric dipole transition intensities in HCl and allow additional assessment of the calculation approach presently used to provide an adequate description of the valence and Rydberg states of HCl. The molecular quantum defect orbital has been applied to the calculation of oscillator strengths. In particular, new insight is given on the assignment of states as the R1Pi, the 1Delta(4dpi and 5ppi), the 1Sigma+(4dpi), and the nddelta(1Pi, 1Phi) and 4f states.
Diatropicity of tetraazanaphthalenes
Tetraazanaphthalenes are diatropic molecules, whose magnetic response to a magnetic field perpendicular to the molecular plane closely resembles that of naphthalene. The out-of-plane component of the magnetic susceptibility tensor and its strong anisotropy can be used as quantifiers of magnetic aromaticity. Maps showing streamlines and modulus of the current density field provide clear evidence for diatropicity of these systems. They also explain the strong anisotropy of carbon and nitrogen magnetic shielding, which is determined by the big out-of-plane component of the nuclear shielding tensor. The electronic ring currents observed in the map deshield the nuclei of ring hydrogens by enforc…
Can aromaticity be connected with molecular polarizability? A theoretical study of benzene isomers and five-membered heterocyclic molecules
Extended calculations of molecular electric dipole polarizability tensor, at Hartree-Fock and correlated level of accuracy (MP2, CCS, CC2, CCSD, and CCSD(T)) have been carried out to investigate whether aromaticity could be related to the electric dipole polarizability of planar ring systems. The calculations prove the exaltation of the average property of conjugated molecules, which is possibly due to their easily polarizable π-electron cloud. On the other hand, theoretical out-of-plane polarizability components are smaller in benzene than in any other C$_6$H$_6$ isomer. The aromatic stabilization energies of monosubstituted five-membered conjugated cyclic molecules increase in the same di…
Carbon nanorings: A challenge to theoretical chemistry
High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions - caused by the polarization associated to curved Ï-conjugated systems - and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the …
The ring-current model of the paratropic pentalene molecule
The ring-current model for the pentalene molecule has been constructed by ab initio techniques. The current density vector field has been used to obtain magnetic shielding density maps for the different protons. It is shown that the paramagnetic flow of the π electrons causes an increase of the out-plane component of proton shielding tensors, that is overall shielding. Distant portions of the π flow also shield carbon nuclei.
Reply to comment on “A MRCI PS and CASSCF study of the ground state MgO dissociation energy”
To compute the dissociation energy of MgO, the relationship among the size of the active space in CASSCF wavefunctions, the computed De and the continuity of ∂E/∂r is studied. Basis set influence is also considered. Finally, it is concluded that the dissociation energy of MgO referred to ground state atoms is 2.32±0.1 eV.
A MRCI PS and CASSCF study of the ground state MgO dissociation energy
Abstract Ab initio calculations at CASSCF and MRCI PS levels are used to determine the dissociation energy for the X 1 Σ + state of MgO, which adiabatically dissociates to the ground state 1 S g of magnesium and to the excited 1 D g state of oxygen, as well as other spectroscopic parameters. Emphasis is placed upon the problem of properly selecting an adequate active space in CASSCF calculations and upon the improvements obtained in MRCI by selecting perturbatively the most important contributions to the total wavefunction and evaluating the remaining ones only by perturbational method. Through a procedure based on stabilizing the computed dissociation energy, values of 3.87 eV (MRCI PS) an…
Potential models for the simulation of methane adsorption on graphene: development and CCSD(T) benchmarks
Different force fields for the graphene–CH4 system are proposed including pseudo-atom and full atomistic models. Furthermore, different charge schemes are tested to evaluate the electrostatic interaction for the CH4 dimer. The interaction parameters are optimized by fitting to interaction energies at the DFT level, which were themselves benchmarked against CCSD(T) calculations. The potentials obtained with both the pseudo-atom and full atomistic approaches describe accurately enough the average interaction in the methane dimer as well as in the graphene–methane system. Moreover, the atom–atom potentials also correctly provide the energies associated with different orientations of the molecu…
Assessment for the mean value total dressing method: Comparison with coupled cluster including triples methods for BF, NO+, CN+, C2, BeO, NH3, CH2, H2O, BH, HF, SiH2, Li2, LiNa, LiBe+, NeH+, and O3
Limited previous experience with the mean value total dressing (MVTD) method had shown that MVTD energies for closed shell systems are generally better than CCSD(T) ones compared to FCI. The method, previously published as total dressing 2′(td-2′), is based on the single reference intermediate Hamiltonian theory. It is not a CC method but deals in a great part with the same physical effects that CC methods that incorporate amplitudes of triples such as CCSDT or its CCSDT-1n approaches. A number of test calculations comparing to diverse CC methods, as well as FCI and experiment when available, have been performed. The tests concern equilibrium energies in NH3 and CH2, equilibrium energies an…
Assessment of the CTOCD-DZ methodin a hierarchy of coupled cluster methods
Gauge origin independent calculations of nuclear magnetic shielding tensors are carried out inside the formalism of the continuous transformation of the origin of the current density leading to formal annihilation of its diamagnetic contribution (CTOCD-DZ). We employ the unrelaxed linear response approach with a hierarchy of different coupled cluster methods in order to assess the importance of the level of approximation in the coupled cluster expansion. The basis set dependence of the computed nuclear magnetic shielding constants is also analyzed in the series of correlation consistent basis sets, with the aim of designing optimized basis sets of relatively small size.
Excitation energies and photoabsorption oscillator strengths of the Rydberg series in CF3Cl. A linear response and quantum defect study.
Vertical excitation energies of the CF(3)Cl molecule have been obtained from a response function approach with a CC reference function to determine absolute photoabsorption oscillator strengths in the molecular-adapted quantum defect orbital formalism (MQDO). The present work covers more highly excited Rydberg states than have been experimentally reported. Assessing of the reliability of the present calculations is provided through a comparative analysis between the results of the molecule and the Cl atom. This can be used to allow for predictions of the same type of properties in other analogous systems.
Size-consistent ab initio calculation of the electric quadrupole moment of Cl2
Abstract The molecular electric quadrupole moment ( Θ ) of Cl 2 has been calculated using SDCI, and (SC) 2 -SDCI wave functions as well as CCSD, CCSD(T), and CC3 methods. All these correlation methods are single reference. All of them, but SDCI, are free of the size-extensivity error. The variation of Θ from the separated atoms to the equilibrium region is reported. The present results leads to an estimated value of 2.3520 a.u. (10.55 × 10 −40 Cm 2 ) corresponding to a CC(3) calculation at the CBS approach and including the ro-vibrational and thermal averaging corrections. This value is compatible with two experimental values and points to one of them as slightly more reliable.
Polarizabilities of small annulenes from Cholesky CC2 linear response theory
Using recently developed algorithms based on Cholesky decomposition of two-electron integrals to compute response properties at the correlated level, the static and dynamic (at 589 nm) polarizabilities of [4n + 2]-annulenes (n = 1, 2, 3, 4) have been calculated. The results show that the perpendicular component increases along the series linearly with the number of double bonds. The in-plane static polarizability is also increasing linearly with the area of the aromatic ring in the case of the delocalized species. However, linearity is lost for the localized conformations and for the dynamic polarizability. (C) 2004 Elsevier B.V. All rights reserved.
Multi-scale theoretical investigation of molecular hydrogen adsorption over graphene: coronene as a case study
The physisorption of molecular hydrogen onto coronene is studied using a multi-scale theoretical approach with Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations. We consider two different kinds of model conformation for the approach of hydrogen towards the coronene i.e., systematic and random. For the systematic attack of hydrogen over coronene, the resulting potential energy profiles from DFT analysis are further found to resemble the Morse potential, and even the highly flexible Murrell–Sorbie (M–S) potential. The resulting M–S fitting also shows a zero-point energy correction of ∼16–17%. On the other hand, the potential energies from the random approach…
Theoretical spectroscopic parameters of the alkali monofluorides LiF, NaF and KF
Abstract Multireference configuration interaction and second-order perturbation theory are used to determine accurate spectroscopic parameters for the ground state of the alkali monofluorides from LiF to KF. Systematic saturation of the spdf subspaces of the atomic basis sets for the electron affinity of fluorine and the ionization potential of the metals have been shown to be more efficient than for the approximate dissociation energies in the molecule. the calculated rotational and vibrational constants and transitions for the three systems show excellent agreement with the expeirmental data.
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. II. Furo-furan Isomers
Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two furan units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been computed by several approximated techniques and a large Gaussian basis set to achieve near Hartree–Fock estimates. Ab initio models of the ring currents induced by a magnetic field normal to the molecular plane were obtained for the three isomeric systems of higher symmetry, showing that the π electrons give rise to intense diamagnetic circulation. The π currents are responsible for enhanced magnetic anisotropy and strong out-of-plane proton deshielding. The theoretical findings are used to build up a “diatropicity …
Binding and isomerization energies for the Cu/CN and Cu(I)CN interactions
Abstract Binding and isomerization energies of the CuCN, CuNC, CuCN+, and CuNC+ systems were investigated by means of a multireference CI perturbatively selected, MRCI-PS approach. The inclusion of the main dynamical correlation effects are evaluated. The binding energies for CuCN and CuNC are 4.37 and 4.03 eV, respectively, and those for CuCN+ and CuNC+ are 0.08 and 1.61 eV. Calculated isomerization energies are 7.86 and 35.98 kcal/mol for CuCN and Cu(I)CN isomerizations, respectively.
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. III. Thieno-thiophene isomers
Near Hartree–Fock values of the magnetic susceptibility and nuclear magnetic shielding of bis-heteropentalenes consisting of two thiophene units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been estimated via computational schemes relying on continuous transformation of the origin of the current density within the coupled Hartree–Fock approximation and extended gaugeless Gaussian basis sets. The results are compared with those obtained via London gauge-including orbitals. Maps of streamlines and the modulus of the ring current density induced by a magnetic field normal to the molecular plane are reported for the three isomers of higher symmetry, showing that the intense diamagnetic…
MP2 Study of Physisorption of Molecular Hydrogen onto Defective Nanotubes: Cooperative Effect in Stone–Wales Defects
We use large-scale MP2 calculations to investigate the physisorption of molecular hydrogen on (9,0) defective carbon nanotubes (CNTs) of C72H18. These large (supra)molecular systems are typically studied using conventional DFT methods, which do not describe well the van der Waals interactions responsible for this process. Here we use CCSD(T)-calibrated MP2 calculations to estimate binding energies by considering four defective structures (hydrogenated divacancy, octagon-pentagon, and two Stone-Wales defects). The largest physisorption energies for the nondefective CNT are for configurations in which H2 points toward the center of one ring. The computed interaction energies for defect-free C…