On the molecular electric quadrupole moment of C2H2 (original) (raw)
Related papers
Journal of Molecular Structure, 2000
The quadrupolarity of carbon dioxide has been studied with higher level ab initio methods. Carbon dioxide exhibits {2 1 2} quadrupolarity in all directions and an explanation is provided of the origin of the sign of the diagonal elements Q ii. The quadrupole moment tensor has been computed using restricted Hartree±Fock theory, second-order Mùller±Plesset perturbation theory and quadratic con®guration interaction theory. A variety of basis sets have been employed up to basis sets of the type [5s, 4p, 2d, 1f] (23s, 8p, 2d, 1f). The quadrupole moment tensor component Q k of carbon dioxide falls in the range between 218.5 and 220.5 Debye A Ê. The quadrupole moment tensor components Q ' of carbon dioxide are smaller, ranging from 214.5 to 215 Debye A Ê , and they are less sensitive to the choice of the theoretical model. The correlated methods consistently predict an increase of Q k while they predict a more modest reduction of Q '. It is for the opposing electron correlation effects on Q k and Q ' that the average values of the diagonal elements, kQ ii l, are essentially independent of the method and exhibit only a small variation depending on the basis set. On the other hand, the anisotropy of the quadrupolarity, the quadrupole moment Q, is affected most by the opposing electron correlation effects on Q k and Q '. The accurate reproduction of the measured quadrupolarity Q 24.3 Debye A Ê requires a theoretical model that employs both a good method and a good basis set. The results suggest that the use of second-order Mùller±Plesset perturbation theory in conjunction with well-polarized triple-z basis sets provides a cost-effective and quite accurate method for the estimation of correlation effects on quadrupole moments.
Electric quadrupole moments and electron affinities of atoms from H to Cl: a coupled-cluster study
Chemical Physics Letters, 1998
Electric quadrupole moments and electron affinities of ground-state atoms from H to Cl are computed at the infinite-order Ž Ž .. Ž . coupled-cluster method with the noniterative CCSD T and iterative CCSDT inclusion of all single, double, and triple excitations, respectively. Generally, there exists some correlation between the magnitudes of quadrupole moments and Ž . electron affinities A of the atoms. The highest level of our calculations delivers an accuracy in the computed A values compared to experimental data not worse than 0.03 eV. q
Molecular quadrupole moments of HCCH, FCCF, and ClCCCl
International Journal of Quantum Chemistry, 2003
The molecular quadrupole moments of HCCH, FCCF, and ClCCCl have been studied as a function of basis set at the self-consistent field, density functional theory (B3LYP), and CCSD(T) levels. The CCSD(T) results, in units of ea 0 2 , are 4.856 (HCCH), Ϫ0.6389 (FCCF), and 3.7685 (ClCCCl). When corrected for vibration, the HCCH result is reduced to 4.795 and is in excellent agreement with experiment, 4.71 Ϯ 0.14. There are no experimental data for FCCF and ClCCCl. The molecular quadrupole moments are shown to have the form ⌰ ϭ ⌰ atoms ϩ ⌰ cr , where ⌰ atoms is the sum of the quadrupole moments of the separated atoms and ⌰ cr is the contribution due to charge redistribution upon molecule formation. This model accounts for the magnitude and signs of ⌰ in this series.
Chemical Physics Letters, 2001
Highly accurate values of the molecular electric quadrupole moment H referring to the centre-of-mass of hydrogen uoride have been determined by means of sophisticated ab initio methods. Our best equilibrium result ± obtained as the full con®guration interaction basis-set limit value augmented with a semi-relativistic correction ± is H e 1:7121 AE 0:0006 a:u: 7:681 AE 0:003 Â 10 À40 C m 2 . The corresponding rovibrationally corrected quadrupole moment H v0;J1 1:7691 AE 0:0006 a:u: 7:937 AE 0:003 Â 10 À40 C m 2 compares very favourably with the experimental value H v0;J1 7:87 AE 0:10 Â 10 À40 C m 2 . Ó
Theoretical Study of the Quadrupolarity of Carbodiimide †
The Journal of Physical Chemistry A, 2002
The quadrupolarity of carbodiimide, HNdCdNH, has been studied in comparison to carbon dioxide. Both heterocumulenes exhibit {-+-} quadrupolarity in all directions. Concepts are formulated to develop an understanding of the origins of quadrupole moments and to trace theoretical level effects to the underlying changes of the electron density. The quadrupole moment tensors have been computed using RHF, MP2 and QCISD theory as well as the B3LYP density functional method. A variety of basis sets have been employed, the two best basis sets are of the types [5s, 4p, 2d, 1f] (23s, 8p, 2d, 1f) and [5s, 4p, 3d, 1f] (12s, 6p, 3d, 1f). The results suggest that the MP2 and B3LYP methods in conjunction with well-polarized triple-basis sets provide a cost-effective and quite accurate method for the estimation of correlation effects on quadrupole moments. The quadrupole moment tensor component Q xx of carbodiimide falls between-16 and-18 DÅ. The components Q yy and Q zz , are similar and they range from-16.5 to-17.5 DÅ and from-17 to-18 DÅ. The correlated methods consistently predict an increase of Q xx , whereas they predict a more modest reduction of Q yy and Q zz. It is for these opposing correlation effects that the average values of the diagonal elements, , are essentially independent of the method and exhibit only a minor basis set dependence. The traceless quadrupole moment of carbon dioxide, Θ) Q ||-Q ⊥ , is-4.3 DÅ. In stark contrast, all of the Θ ii values of carbodiimide are close to zero and only the off-diagonal quadrupole moment element Θ xy is quite large with Θ xy)-6.2 DÅ.
Chemical Physics Letters, 2007
Commonly used exchange-correlations functionals are known to produce inaccurate electric field gradient (EFG) values at the nuclei of transition metals and heavy atoms in molecular calculations. This makes density functional theory (DFT) essentially inapplicable for the determination of nuclear quadrupole moments (NQM) from absolute EFG estimates. However, in a recently proposed indirect approach, the NQM is determined from the changes in the EFG along a series of molecules. We investigate this indirect approach within four-component relativistic DFT, showing that, at least in a series of chemically strictly related molecules, EFG variations can be computed quite accurately. This leads to surprisingly stable and reliable estimates of the NQM, even in notoriously 'difficult' cases such as 197 Au.