Theoretical Investigation For One-dimensional Monatomic Chains Of V, Co And Their 1D Alloy Atomic Chains

In recent years, quasi one-dimensional materials have attracted great attentions in the scientists in the fields of physics, chemistry and material because of their special configurations and peculiar characteristics. The one-dimensional atomic chains systems are the test platform to proof the ready-made theory of three-dimensional systems, and the important foundation to investigate the atomical structures, mechanical and electrical properties of real nanowires. The research to one-dimensional metal atomic chains also promotes to understand the detail stretching process from nanowires to atomic chains. Since the stable gold monatomic chains suspended between two gold electrodes had realized in laboratories by two research groups nearly at the same time, the researches to the structural properties of low-dimensional atomic chains systems have become one of important research subjects in the fields of material and physics.The electron configurations of the transitional-metal vanadium and cobalt atoms are 3d~34s~2 and 3d~74s~2 respectively, that is they are complemented with each other. In this dissertation, we have studied the structural stability and the related properties of the pure atomic chains and alloy ones which formed with transitional-metal vanadium and cobalt atoms. It is expected that the study will provide powerful theoretical guidance for the preparing of materials, controlling, popularizing and applying of systematic structures'growth to everyone.In Chapter one, we mainly introduce the research progress on the quasi one–dimensional metal atomic chains, at the same time, we give the research objects in this dissertation. In chapter two, we briefly present the theory, scientific computational methods and software package used in the dissertation. In the first place, we introduce the density functional theory(DFT), exchange-correlation functional; then, interpret pseudopotential and plane-wave basis set; Finally, we introduce the quantum chemistry software(Vienna ab initio simulation package) (VASP is abbreviate to it).In Chapter three, we investigate the structural stability and electromagnetic properties of the 1D monoatomic chains of vanadium and cobalt on the base of Density Functional Theory. The results are as follows: 1) The cobalt atoms can form five stable one-dimensional chains in linear, dimerization, zigzag, ladder and double zigzag structures. Whereas, cobalt can form one-dimensional chains in linear, dimerization, two kinds of zigzag and ladder. 2) In contrast to uniform metallic charge density of bulk, the bonding in the one-dimensional structures of vanadium acquires directionality, the charges are accumulated between atoms forming a directional bond in the vanadium chains. However, there are no obvious directional bonds in the cobalt chains. The valence electrons are delocalized as similar to the charge density of cobalt bulk. 3) Among the series of one-dimension vanadium chains studied, the linear chain is the most unstable structure, while the zigzag chain with a unit rather close to an equilateral triangular geometry is most favorable, the others are all in metastable. However, among the cobalt chains, the ladder chain is most stable structure, and the dimerization chain is most unfavorable which is slightly worse than the linear one. 4) The one-dimension chains of vanadium have not magnetic property in the case of spin-polarization. While the cobalt's conditions differ from vanadium's, that is the cobalt chains in linear show a non-magnetism state in the case of spin-polarization, and the ladder ones show a weak magnetism state. However, the cobalt chains in dimerization show strong ferromagnetism, and zigzag ones have both ferromagnetism and antiferromagnetism.In chapter four, we investigate the structure stability and electronic structures of one-dimensional alloy VCo chains by using the first-principle calculation based on the Density Functional Theory. By comparing the binding energy of one-dimension V, Co and VCo chains, we can find that the alloy VCo chains are more stable than the corresponding pure Co chains, but less stable than the pure V chains.