Dynamic polarizabilities of rareearthmetal atoms and dispersion coefficients for their interaction with helium atoms
Abstract
The dynamic scalar and tensor polarizabilities of the rareearthmetal atoms are calculated with timedependent density functional theory. The frequencydependent polarizabilities at imaginary frequencies are used to determine the isotropic and orientationdependent van der Waals coefficients for the interactions of the rareearthmetal atoms with helium atoms. The static polarizabilities are compared with other theoretical values and with experimental results. The agreement is satisfactory in most cases but there are some exceptions where the discrepancy between theory and experiment is significant. The derived isotropic van der Waals coefficients range between 37 and 50 E{sub H}a{sub 0}{sup 6} and the orientationdependent coefficients between 2 and 1 E{sub H}a{sub 0}{sup 6}. Thus the ratio of elastic to inelastic scattering cross sections is expected to be substantial and any one of the rareearthmetal atoms is an excellent candidate for trapping and cooling in a He gas.
 Authors:
 Department of Chemistry, University of Montana, Missoula, Montana 59812 (United States)
 (United States)
 (Netherlands)
 Publication Date:
 OSTI Identifier:
 20982343
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review. A; Journal Volume: 75; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevA.75.032723; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 74 ATOMIC AND MOLECULAR PHYSICS; ATOMATOM COLLISIONS; ATOMS; COOLING; CROSS SECTIONS; DENSITY FUNCTIONAL METHOD; FREQUENCY DEPENDENCE; HELIUM; INELASTIC SCATTERING; INTERACTIONS; POLARIZABILITY; RARE EARTHS; TIME DEPENDENCE; TRAPPING; VAN DER WAALS FORCES
Citation Formats
Chu, Xi, Dalgarno, Alexander, Groenenboom, Gerrit C., ITAMP, HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen. Dynamic polarizabilities of rareearthmetal atoms and dispersion coefficients for their interaction with helium atoms. United States: N. p., 2007.
Web. doi:10.1103/PHYSREVA.75.032723.
Chu, Xi, Dalgarno, Alexander, Groenenboom, Gerrit C., ITAMP, HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, & Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen. Dynamic polarizabilities of rareearthmetal atoms and dispersion coefficients for their interaction with helium atoms. United States. doi:10.1103/PHYSREVA.75.032723.
Chu, Xi, Dalgarno, Alexander, Groenenboom, Gerrit C., ITAMP, HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen. Thu .
"Dynamic polarizabilities of rareearthmetal atoms and dispersion coefficients for their interaction with helium atoms". United States.
doi:10.1103/PHYSREVA.75.032723.
@article{osti_20982343,
title = {Dynamic polarizabilities of rareearthmetal atoms and dispersion coefficients for their interaction with helium atoms},
author = {Chu, Xi and Dalgarno, Alexander and Groenenboom, Gerrit C. and ITAMP, HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 and Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen},
abstractNote = {The dynamic scalar and tensor polarizabilities of the rareearthmetal atoms are calculated with timedependent density functional theory. The frequencydependent polarizabilities at imaginary frequencies are used to determine the isotropic and orientationdependent van der Waals coefficients for the interactions of the rareearthmetal atoms with helium atoms. The static polarizabilities are compared with other theoretical values and with experimental results. The agreement is satisfactory in most cases but there are some exceptions where the discrepancy between theory and experiment is significant. The derived isotropic van der Waals coefficients range between 37 and 50 E{sub H}a{sub 0}{sup 6} and the orientationdependent coefficients between 2 and 1 E{sub H}a{sub 0}{sup 6}. Thus the ratio of elastic to inelastic scattering cross sections is expected to be substantial and any one of the rareearthmetal atoms is an excellent candidate for trapping and cooling in a He gas.},
doi = {10.1103/PHYSREVA.75.032723},
journal = {Physical Review. A},
number = 3,
volume = 75,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}

The dynamic scalar and tensor polarizabilities of Sc and Ti are computed with timedependent density functional theory. These polarizabilities are used to compute the isotropic and anisotropic dispersion interactions in ScHe and TiHe. We find C{sub 6,0}(ScHe)=30.00, C{sub 6,2}(ScHe)=1.63, C{sub 6,0}(TiHe)=28.40, and C{sub 6,2}(TiHe)=0.90 (E{sub h}a{sub 0}{sup 6}). We show that an estimate of the dispersion anisotropy based on static polarizabilities results in an overestimation by a factor of 2.

Dispersion coefficients for H and He interactions with alkalimetal and alkalineearthmetal atoms
The van der Waals coefficients C{sub 6}, C{sub 8}, and C{sub 10} for H and He interactions with the alkalimetal (Li, Na, K, and Rb) and alkalineearthmetal (Be, Mg, Ca, and Sr) atoms are determined from oscillator strength sum rules. The oscillator strengths were computed using a combination of ab initio and semiempirical methods. The dispersion parameters generally agree with close to exact variational calculations for LiH and LiHe at the 0.1% level of accuracy. For larger systems, there is agreement with relativistic manybody perturbation theory estimates of C{sub 6} at the 1% level. These validations for selected systems attestmore » 
Dipole polarizabilities of excited alkalimetal atoms and longrange interactions of ground and excitedstate alkalimetal atoms with helium atoms
The scalar and tensor dynamic polarizabilities of the first excited {sup 2}P{sub 1/2,3/2} states of the alkalimetal atoms Na, K, and Rb are calculated using relativistic manybody perturbation theory. Comparison with experimental measurements of the static polarizabilities suggests that the errors in the theoretical predictions do not exceed 1%. The dynamic polarizabilities at imaginary frequencies are employed to calculate the longrange van der Waals coefficients for the interaction of groundstate helium atoms with the excited alkalimetal atoms to a probable error of less than 2%.