Three-body Dispersion Coefficients Research Articles

Higher order two- and three-body dispersion coefficients for alkali isoelectronic sequences by a variationally stable procedure

Using the variationally stable method of Gao and Starace, and the simple ground state wave function of the valence electron previously suggested by Patil and Tang, the multipolar polarizabilities of Li, Na, K, Rb, Cs, Be(+), Mg(+), Ca(+), Sr(+), Ba(+), the two-body dispersion coefficients of homonuclear and heteronuclear interactions from C(6) to C(40), as well as the three-body dispersion coefficients Z(L(1), L(2), L(3)) (up to L(i) = 5), are investigated. Higher order van der Waals dispersion coefficients C(n) (n > 24) and Z(L(1), L(2), L(3)) (L(i) > 3) are reported for the first time. Comparisons with previous calculations found in the literature show that this approach is capable of yielding precise and fast convergent values for higher order dispersion coefficients for alkali-metal atoms.

Three-Body Dispersion Coefficients for Excited Hydrogen Atoms

The three-body van der Waals dispersion coefficients Z(l 1 l 2 l 2 ) (up to l i =5) for the H(1s)-H(1s)-H(1s) and H(2s)-H(2s)-H(2s) systems are calculated by virtue of the dynamic polarizabilities at imaginary photon frequencies. The expression for the 2 l -pole dynamic polarizabilities of atomic hydrogen is derived by application of the integration properties of the one-dimensional radial Coulomb Green's function. The results for the H(1s)-H(1s)-H(1s) system are consistent with previous calculation in the literature, while the results for the H(2s)-H(2s)-H(2s) systems are reported for the first time, and they are the main contribution of this work. PACS: 32.21.DK, 34.20.Cf

Dispersion coefficients and frequency-dependent polarizabilities

Extensions of previous methods for obtaining two- and three-body dispersion coefficients are presented. Many-dimensional arrays in inner projections are utilized. The required matrix elements are expressed in terms of atomic frequency (Cauchy) moments. Approximate dynamic polarizabilities are derived using generalized inner projections, and a number of theorems for definite operators are extended to more general cases. Numerical results for both two- and three-body dispersion coefficients are reported.

High precision calculation of multipolar dynamic polarizabilities and two- and three-body dispersion coefficients of atomic hydrogen

In this paper we investigate a variationally stable procedure for multipolar dynamic polarizabilities calculation as well as the two- and three-body van der Waals coefficients of the hydrogen atom. This approach provides precise, fast convergent values for real and imaginary frequency-dependent 2 L -pole dynamic polarizabilities. Highly accurate two- and three-body van der Waals dispersion coefficients are calculated from dynamic polarizabilities at imaginary photon frequencies. The present approach is also precise for higher interaction orders. The results are compared with previous calculations found in the literature.

Ab initio calculations of dispersion coefficients for nucleic acid base pairs

The results of ab initio calculations of two- and three-body dispersion coefficients for the four most important nucleic acid bases are reported. The isotropic as well as anisotropic coefficients were found by using the time-dependent Hartree-Fock approach and the aug-cc-pVDZ basis set. Single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD(T)] was used to find the values of static polarizabilities which were subsequently used to estimate the values of the CCSD(T) dispersion coefficients. A comparison of these estimated CCSD(T) dispersion coefficients with coefficients found by using empirical approaches based on atomic contributions revealed that the latter are not reliable.

A simple method for calculating dispersion coefficients for isolated and condensed-phase species

A simple method is developed for the derivation of two-body and three-body dispersion coefficients for isolated and in-crystal atoms from a knowledge of their dipole polarizability and effective number of electrons. The method is checked by comparison with a large body of published theoretical results.

Three-body dispersion coefficients for alkali-metal atoms

We study the nonadditive part of the long-range interaction among three alkali-metal atoms in their ground states. Using nondegenerate perturbation theory, up to the third order, we have computed the dispersion coefficients C for three alkali-metal atoms interacting via their electric dipole moments. Both heteronuclear and homonuclear cases are considered. The numerical values for the C coefficients suggest that such three-body dipole interaction effects may not be neglected in the description of the long-range surface potential interaction for alkali-metal atoms. Furthermore, we show that approximate formulas for C of Midzuno and Kihara [J. Phys. Soc. Jpn. 11, 1045 (1956)] give results in excellent agreement with results of our calculations. Comparisons are given of our results with results of others and with results of other approximate formulas. The effect on our results for the C coefficient of uncertainties in the experimental values of the static dipole polarizabilities, on which our results depend, is also analyzed.

Multipolar polarizabilities and two- and three-body dispersion coefficients for alkali isoelectronic sequences

Using simple wave functions based on the asymptotic behavior and on the binding energies of the valence electron, we have evaluated multipolar matrix elements. They allow us to obtain polarizabilities up to α12 of Li, Na, K, Rb, Cs, Be+, Mg+, Ca+, Sr+, Ba+, and dispersion coefficients of homonuclear and heteronuclear interactions from c6 to c24. Comparisons with previously determined low order quantities show that this approach is capable of yielding quite useful values for these quantities.

Ab initio dispersion coefficients for interactions involving rare-gas atoms

Calculations of the dynamic dipole, quadrupole, and octopole polarizabilities of Ne, Ar, Kr, and Xe are carried out using both time-dependent coupled Hartree–Fock and many-body perturbation theory methods. Dispersion coefficients are calculated for interactions involving these species. The dynamic polarizabilities are combined with previously published dynamic polarizabilities of H, He, H2, N2, HF, and CO to obtain dispersion coefficients for the interactions involving one of these species and one of Ne, Ar, Kr, or Xe. The dipole–dipole dispersion coefficients agree quite well with the best available semiempirical estimates. The isotropic higher multipole coefficients are in reasonable agreement with previous semiempirical estimates where available, and the anisotropic ones are, in most cases, the first reliable ones to appear in the literature. Nonadditive three-body dispersion coefficients for the Ne3, Ar3, Kr3, and Xe3 interactions are also calculated.

One-centre calculation of dispersion coefficients between ground state H atoms from pseudostate decomposition of static multipole polarizabilities

N-term pseudostate decomposition of the exact H atom static polarizabilities allows for one-centre calculation of two-body and three-body dispersion coefficients between ground state H atoms to an accuracy remarkably higher than the previously reported two-centre results. Starting from a simple power basis in the radial variable, the first-order wavefunction of the atom in the external field is expanded into a finite number N of linear pseudostates which diagonalize the matrix of the excitation energies. The expansion is rapidly convergent, and if for N = 5 the numerical results are exact to 6 significant figures, the 20-term approximation gives coefficients which are accurate to the 15th decimal place. The method can be viewed as a generalization of the Slater-Hasse-Kirkwood approximation in the context of a hypergeneralized London formula.

Calculations of two- and three-body dispersion coefficients for ions in crystals

Coupled Hartree-Fock theory is used to calculate two and three body dispersion coefficients for in-crystal ions (Li+, Na+, K+, Rb+, Mg2+, Ca2+, F-, Cl-, O2-) subject to both electrostatic and overlap interactions. For anions the reduction of the dispersion coefficients in the crystalline environment parallels the decrease of the static polarizability. From comparison of ab initio results with those of the Slater-Kirkwood formula we propose an empirical scheme for calculating in-crystal dispersion coefficients from accurate static polarizabilities. We find that two-body dispersion forces are not responsible for the greater stability of the 8 : 8 compared to the 6 : 6 polymorph of CsCl. A correlated Moller-Plesset calculation of the static polarizability of Rb+ confirms our previous scheme for deriving polarizabilities from experiment.

The generator coordinate method applied to variational perturbation theory. Multipole polarizabilities, spectral sums, and dispersion coefficients for helium

It is shown that a suitable variant of the generator coordinate method can be used for accurate variational perturbation theory calculations. The test problems chosen are calculations of the dipole, quadrupole, and octupole polarizabilities, spectral sums, two-body dispersion coefficients, and nonadditive three-body dispersion coefficients for the ground state of atomic helium. An accurate explicitly correlated wave function for the unperturbed problem is utilized along with explicitly correlated basis functions for the pseudospectra. The dipole results are in excellent agreement with previous high accuracy calculations. The quadrupole and octupole results are expected to be the most accurate ones currently available. Estimates of some hexadecapole properties are made.