Adsorption and dissolution of nitrogen in lithium : QM DFT investigation

Abstract Ab initio quantum mechanic density functional theory (QM DFT) calculations were used to study the interaction of molecular nitrogen (N 2 ) with metallic Li surface. The calculation has been made using Dmol commercial package provided by Accelrys Inc. A clusters of metal atoms, of various sizes were used to study the interaction of nitrogen with Li surface. It was demonstrated that the size is large enough to reach the asymptotic regime. The cluster had one, two, three and four atomic layers. It was also shown that due to low-cohesion energy of Li, the cluster had to be supported by external forces and/or limitation on atomic displacement of the atoms in the cluster. The interaction of single N atom with the Li surface was investigated. As it is expected, a single N atom is strongly attracted by the surface. A N 2 molecule interaction with Li surface was also investigated. In contrast to Al, Ga or In surfaces, in case of Li surface, the N 2 molecule is adsorbed in the molecular state, i.e. no dissociation of molecular nitrogen in the adsorption stage occurred. The N 2 adsorption process is barrierless, with the energy level for the physisorbed state about 0.5 eV below the far distance level. From the surface state, the N 2 molecule can penetrate into the lithium interior. The barrier for this transition is about 0.2 eV. It was also found that the energy of the molecular nitrogen dissolved in the Li is about 1.3 eV below the far distance level. The interatomic N–N distance on the N 2 molecule located in the Li interior is only slightly increased to 1.25 A, which is 0.15 A larger than the standard 1.1 A distance for the free N 2 molecule. This confirms that the adsorption and dissolution of nitrogen in Li does not lead to the decomposition of the molecular N 2 structure.