Non-collinear relativistic DFT calculations for small molecules

During the last 15 years a lot of effort has been invested in the experimental investigation of the chemical behaviour of superheavy elements. One was able to show that the general feature of the elements 104 to 108 is to follow the trend of the continuation of the Periodic Table [1]. Details of the experimental methods and results can be found in the recent review by Schädel [2]. These elements are so heavy that any non-relativistic calculation can not give a realistic prediction so that a full relativistic calculation is the only appropriate method. Details of the theoretical methods and results can be found in the review by Pershina [3]. The theoretical as well as the experimental effort now concentrates on the investigation of the chemical behaviour of the elements beyond 110. In this region of elements up to now nothing is known experimentally. The nuclear chemists concentrate on the chemistry of element 112. They have set up an experiment to investigate the adsorption of this element relativ to the homologue Hg and the noble gas Rn. Positive results of those experiments have recenly been reported [4]. During the last years we have investigated theoretically the adsorption energy of element 112 and Hg on a Au surface. The newest results predict an adsorption energy of about 0.7 eV [5] which is somewhat below Hg but reasonably higher than that of Rn. Because all these elements between 110 and 119 now become interesting, the effort from the theoretical side concentrates on the calculation of small molecules with superheavy elements. These kind of calculations together with analogue calculations for their homologues allow further predictions of their chemical behaviour. Various methods have been used so far. A few references including results for even heavier elements can be found in Ref. [6-10]. Our method of calculation is a full relativistic 4component molecular code which now includes the possibility to calculate these systems in a non-collinear fashion. This method allows the magnetic density distribution to show in different directions in different regions of the molecule. This is connected with different total energies and thus modifies the binding energies of the molecules compared to the collinear method which is used up to now. Table 1 lists the binding energies De, the bond distances Re and frequencies ωe for a few superheavy molecules with element 111 and 113. For the diatomic molecule (111)2 the potential energy curve in different approximations is given in Fig. 1. These values are important ingredients in order to understand the chemical behaviour of these elements which are dominated by large direct relativistic effects for the 7p1/2 electrons and large spin-orbit splitting of the 7p-shell in the case of element 113.