Analytic high-order Douglas-Kroll-Hess electric field gradients

摘要

In this work we present a comprehensive study of analytical electric field gradients in hydrogen halides calculated within the high-order Douglas-Kroll-Hess(DKH)scalar-relativistic approach taking picture-change effects analytically into account.We demonstrate the technical feasibility and reliability of a high-order DKH unitary transformation for the property integrals.The convergence behavior of the DKH property expansion is discussed close to the basis set limit and conditions ensuring picture-change-corrected results are determined.Numerical results are presented,which show that the DKH property expansion converges rapidly toward the reference values provided by four-component methods.This shows that in closed-shell cases,the scalar-relativistic DKH(2,2)approach which is of second order in the external potential for both orbitals and property operator yields a remarkable accuracy.As a parameter-dependence-free high-order DKH model,we recommend DKH(4,3).Moreover,the effect of a finite-nucleus model,different parametrization schemes for the unitary matrices,and the reliability of standard basis sets are investigated.