Introducing Novel Materials with Diffuse Electrons for Applications in Redox Catalysis and Quantum Computing via Theoretical Calculations

Abstract

Diamond-like structures, where carbon atoms have been replaced with Li+ and C–C bonds with diamines, have currently been introduced as new materials, which can host diffuse electrons in the periphery of each lithium tetra-amine center. These materials display a diverse range of properties behaving as metals or semiconductors depending on the diamine chain length. Multi-reference wavefunction and density functional theory calculations were employed to study the electronic structure of these materials. Initially, gas phase calculations are performed on isolated (NH3)3LiNH2(CH2)1–10H2NLi(NH3)3 molecular strings. One diffuse electron surrounds the periphery of each −NH2Li(NH3)3 terminus. The two terminal electrons couple into a triplet and open-shell singlet states, which are nearly degenerate for long chains and as closed shell singlets for short. At intermediate lengths, the wavefunction of the ground-state singlet state mixes both open- and closed-shell configurations raising doubts about which configuration should be considered for density functional theory calculations. Observations from gas phase calculations accurately predict properties from the condense phase density functional theory calculations carried out for proposed crystalline Li-diamine materials, offering an avenue for further development and insight. Spin-polarized and unpolarized calculations are performed for the whole range of hydrocarbon sizes reporting geometrical and electronic band structures, spin density contours, and density of states. Diffuse electrons can be used for redox reactions or can serve as qubits for quantum computing. Future work will focus on decorating the hydrocarbon backbone with functional groups and/or bulky units, in order to facilitate or block the association between neighboring electrons for more controlled quantum computing applications and propose materials for selective redox catalysis.

A fresh perspective on metal ammonia molecular complexes and expanded metals: opportunities in catalysis and quantum information

“…A recently proposed system is offered through the use of diamines to link two SEP species together. 47 From this, one can make MOF-type (MOF = metal–organic-framework) materials composed of metal centers with diffuse peripheral electrons. The first system of this type to be studied consists of lithium-diamine-lithium bridges in a diamond-like arrangement (see Fig.…”

“…Short hydrocarbon backbones favor metallic behavior (similar to unbridged SEPs/expanded metals), while longer ones bear small band gaps pointing to semiconducting behavior. 47…”

“…Going into more detail, a linked-SEP with two lithium centers, such as (NH 3 ) 3 Li−NH 2 (CH 2 ) n H 2 N−Li(NH 3 ) 3 with n = 1–10, 47 can also be viewed as two H atoms kept fixed at a specific distance defined by n . Therefore, the two remote electrons in the case of n = 10 couple into degenerate triplet and singlet states.…”

“…As a result the coupling of the two electrons in a closed-shell singlet occurs only at very short hydrocarbon chains for Be (as evidenced by the abrupt change from n = 2 to n = 1 for Be–C and gradual change from n = 4 to n = 1 for Li–N combinations). 47,126…”

“…It has been shown recently that the commonly used density functional theory calculations under periodic boundary conditions can severely fail in describing the spin coupling of neighboring diffuse electrons. 47 Since multi-configurational methods for periodically repeated systems (necessary in such cases) are not currently available or practical, density functional theory calculations should be used with caution.…”