The molecular electric quadrupole moment and electric-field-gradient induced birefringence (Buckingham effect) of Cl_2. - Chiara Cappelli; Ulf Ekström; Antonio Rizzo; Sonia Coriani (J. Comput. Methods Sci. Eng., 2004)

Internal-to-cartesian back transformation of molecular geometry steps using high-order geometric derivatives. - Vladimir V. Rybkin; Ulf Ekström; Trygve Helgaker (J. Comput. Chem., 2013)