Search results for "Configuration interaction"
showing 9 items of 99 documents
Full configuration interaction calculation of the low lying valence and Rydberg states of BeH
2007
The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and qua…
On the dissociation energy of Cu2 and CuH using a differential correlation approach
1990
The energy contributions involved in the “dissociation-consistent configuration interaction” (DCCI) scheme proposed by Goddard and co-workers plus the dispersion effects associated with the valence MOs adjacent to the bond (DISP) are evaluated for the Cu2 and CuH systems, following the “configuration interaction by perturbation with multiconfigurational zeroth-order wavefunction selected by iterative process” (CIPSI) algorithm. Using a relativistic pseudopotential to represent the neon core of copper, and a flexible basis set for the valence shell, the results obtained with the CIPSI/DCCI (+ DISP) approach shows a good agreement with previous theoretical results employing basis sets of simi…
A theoretical study of the electronic spectrum of thiophene
1993
Abstract The electronic spectrum of thiophene has been studied using multiconfiguration second-order perturbation theory and extended ANO basis sets. The calculations comprise four singlet valence excited states and the 3s3p3rd Rydberg series. The lowest triplet states were included and some n-π* and n-σ* states. The results have been used to assign the experimental spectrum below 8.0 eV, with a maximum deviation of about 0.1 eV for vertical transition energies. The calculations place the 2 1A1 valence state at 5.33 eV, below the 1 1B2 valence state at 5.72 eV, and the most intense valence transitions at 6.69 eV (3 1A1) and 7.32 eV (4 1B2) with oscillator strengths 0.19 and 0.39, respective…
Rydberg, valence and mixed states in the vertical spectrum of HF
2009
Abstract Size-consistent self-consistent multireference singles and doubles configuration interaction (SC)2–MR–SDCI, and linear response coupled cluster of singles and doubles including triples LR–CCSDR(3) methods, with a basis set of ANO’s augmented with a single series of molecular Rydberg functions, have been applied to the calculation of vertical excitation energies of HF in the 10–16 eV region. Special care has been put in the description of the valence, Rydberg and mixed states. Some advantage has been taken from the different physical contents of the methods to discuss some assignments. The (4,5) f Rydberg states of HF are predicted at 15.2 and 15.5 eV.
Binding and isomerization energies for the Cu/CN and Cu(I)CN interactions
1993
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.
Dissociation energies within selected configuration interaction and perturbation theory
1993
Abstract Selected configuration interaction (CI) calculations and second-order perturbational theory are used to truncate systematically multireference single and double excitation CI (MRCI) expansions in the calculation of the bond dissociation energies of several systems like the single-bonded LiF molecule or the multiple-bonded N2, NO and O2 diatomic systems. The method is extended to compute the CH bond dissociation energy ofethene C2H4. It is shown how the proposed scheme (perturbation-selected MRCI (MRCI-PS)) is able to reproduce the accuracy of complete MRCI expansions with only a small number of configurations variationally evaluated.
Towards a converged barrier height for the entrance channel transition state of the N(2D)+CH4 reaction and its implication for the chemistry in Titan…
2011
Abstract The N( 2 D) + CH 4 reaction appears to be a key reaction for the chemistry of Titan’s atmosphere, opening the door to nitrile formation as recently observed by the Cassini–Huygens mission. Faced to the controversy concerning the existence or not of a potential barrier for this reaction, we have carried out accurate ab initio calculations by means of multi-state multi-reference configuration interaction (MS-MR-SDCI) method. These calculations have been partially corrected for the size-consistency errors (SCE) by Davidson, Pople or AQCC corrections. We suggest a barrier height of 3.86 ± 0.84 kJ/mol, including ZPE, for the entrance transition state, in good agreement with the experime…
Tin resonance-ionization schemes for atomic- And nuclear-structure studies
2020
This paper presents high-precision spectroscopic measurements of atomic tin using five different resonance-ionization schemes performed with the collinear resonance-ionization spectroscopy technique. Isotope shifts were measured for the stable tin isotopes from the $5{s}^{2}5{p}^{2}\phantom{\rule{0.28em}{0ex}}^{3}{P}_{0,1,2}$ and ${}^{1}{S}_{0}$ to the $5{s}^{2}5p6s\phantom{\rule{0.28em}{0ex}}^{1}{P}_{1},^{3}{P}_{1,2}$ and $5{s}^{2}5p7s{\phantom{\rule{0.28em}{0ex}}}^{1}{P}_{1}$ atomic levels. The magnetic dipole hyperfine constants ${A}_{\mathrm{hf}}$ have been extracted for six atomic levels with electron angular momentum $Jg0$ from the hyperfine structures of nuclear spin $I=1/2$ tin isot…
Excitation Energy-Transfer in the LH2 Antenna of Photosynthetic Purple Bacteria via Excitonic B800 and B850 States
2000
A newly developed CIEM method that uses a combination of semi-empirical or ab-initio configuration interaction methods and exciton theory to predict electronic energies, eigenstates, absorption and CD spectra of aggregated chromophoric systems with environmental interactions included is extended and used for estimation of excitation energy transfer rates. Excitonic energy levels of the two ring systems the B800 and the B850 of the light harvesting antenna LH2 of Rhodopseudomonas acidophila and the corresponding absorption spectrum were calculated by assuming inter-ring interactions to be zero. Excitation energy transfer rates were calculated by using the Fermi Golden rule with the dipole - …