Electron correlation and nuclear charge dependence of parity-violating properties in open-shell diatomic molecules

The scaling of nuclear spin-dependent parity violating effects with increasing nuclear charge $Z$ is discussed in two series of isovalent open-shell diatomic molecules. The parameter $W_{\mathrm{a}}$ characterising the strength of parity violation in diatomic molecules is calculated in the framework of the zeroth-order regular approximation (ZORA) and found to be in good agreement with the $R(Z)Z^k$ scaling law derived for atoms in which $R(Z)$ represents a relativistic enhancement factor. The influence of electron correlation is studied on the molecular level, with spin-polarisation effects being conveniently accounted for by a previously established approximate relation between the hyperfine coupling tensor and $W_{\mathrm{a}}$. For high accuracy predictions of parity violating effects in radium fluoride the necessity for systematically improvable correlation calculations is emphasised.