P. Turski et Aj. Sadlej, The change of picture contribution to relativistic corrections to second-order properties, CHEM P LETT, 338(4-6), 2001, pp. 345-352
The effect of the so-called change of picture for operators in approximate
relativistic theories on the second-order properties arising from some exte
rnal perturbation, is considered. By means of the direct perturbation theor
y the general formula for the lowest-order relativistic correction to secon
d-order properties is derived. The term which arises from the change of pic
ture for the external perturbation operator is identified and evaluated for
dipole and quadrupole polarizabilities. For the 1s(1/2) state of the hydro
gen-like ions this term is found to bring about 16% and 7% of the total low
est-order irelativistic correction to the dipole and quadrupole polarizabil
ities, respectively. This finding is discussed in terms of its importance f
or long range interactions between heavy systems. (C) 2001 Elsevier Science
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