TY - JOUR

T1 - Does scaling or addition provide the correct frequency dependence of β∥(-ωσ; ω1, ω2) at the correlated level? An investigation for six molecules

AU - Dalskov, Erik K.

AU - Jensen, Hans Jørgen Aa

AU - Oddershede, Jens

PY - 1997/1

Y1 - 1997/1

N2 - The frequency dependent polarizability α(-ωσ; ω1) and the frequency dependent first hyperpolarizability β(-ωσ; ω1, ω2) have been calculated using both self consistent field (SCF) and multiconfigurational SCF (MCSCF) linear and quadratic response functions for six small molecules: BH, CO, HF, H2O, NH3, and H2S. Two approximate ways of using the calculated dispersion at the SCF level to describe the frequency dependence at the correlated level, referred to as scaling and addition, have been tested. Calculated frequency dependent MCSCF results are used to investigate the validity of these approximations. Our results indicate that, if the correlation correction to the static average hyperpolarizability is large, then the approximations do not hold. The same conclusion holds if correlation changes the sign of the average first hyperpolarizability at zero frequency. There is also a tendency towards an underestimation of the frequency dependence if scaling or addition is applied. There does not seem to be a simple way to infer anything about the validity of scaling or addition for β∥ from either the lower lying excitations and their intensities or from the frequency dependence of the dipole polarizability.

AB - The frequency dependent polarizability α(-ωσ; ω1) and the frequency dependent first hyperpolarizability β(-ωσ; ω1, ω2) have been calculated using both self consistent field (SCF) and multiconfigurational SCF (MCSCF) linear and quadratic response functions for six small molecules: BH, CO, HF, H2O, NH3, and H2S. Two approximate ways of using the calculated dispersion at the SCF level to describe the frequency dependence at the correlated level, referred to as scaling and addition, have been tested. Calculated frequency dependent MCSCF results are used to investigate the validity of these approximations. Our results indicate that, if the correlation correction to the static average hyperpolarizability is large, then the approximations do not hold. The same conclusion holds if correlation changes the sign of the average first hyperpolarizability at zero frequency. There is also a tendency towards an underestimation of the frequency dependence if scaling or addition is applied. There does not seem to be a simple way to infer anything about the validity of scaling or addition for β∥ from either the lower lying excitations and their intensities or from the frequency dependence of the dipole polarizability.

UR - http://www.scopus.com/inward/record.url?scp=0002061610&partnerID=8YFLogxK

M3 - Journal article

AN - SCOPUS:0002061610

VL - 90

SP - 3

EP - 14

JO - Molecular Physics

JF - Molecular Physics

SN - 0026-8976

IS - 1

ER -