Strong chemical bonds in heavy diatomics: PtSi, PtTh and AuTh+

Ab initio relativistic calculations are reported for the electronic ground states of the known diatomic species PtSi and PtTh, and the unknown isoelectronic species AuTh+. Relativistic effects are treated at the quasirelativistic Douglas–Kroll level and electron correlation at the CASPT2 or CCSD(T) level.