Screening And Design Of Thermodynamically Stable 2D Carbon Structures

Two-dimensional materials are crystalline materials consisting of a single or multiple atomic layer that are only a few nanometers thick or even thinner.In such materials,electrons can move freely in a two-dimensional plane,while their movement in the third direction is confined by quantum mechanics.Two-dimensional materials were proposed along with the successful preparation of a single atomic layer of graphite material,graphene,by the Geim team at the University of Manchester in 2004.Since the discovery of graphene more than ten years ago,two-dimensional carbon materials have been the core focus of materials research.In addition to graphene,researchers have also developed several graphene-like allotropes,of which several have been synthesized in experiments and have been used in applications such as photovoltaics,semiconductors,electrodes,and biological monitoring.Therefore,the search and development of two-dimensional allotropes of carbon is important for both fundamental research and industrial applications.However,at present there is still no theoretical systematic exploration of new two-dimensional carbon materials.This paper intends to theoretically and systematically explore the entire configuration space of two-dimensional carbon allotropes under the framework of "Material Genome Initiative" to find thermodynamically stable two-dimensional carbon materials and enrich the relevant computational material database.Traditional methods of new material structure prediction are either database-based data mining or global optimization,and these methods have their own limitations.This paper uses a new method,the configurational sampling method,to evaluate which theoretically proposed planar carbon allotrope can be experimentally realized.The key idea is that the frequency of occurrence of allotropes measures the synthesizability in experiments.The frequency of occurrence can be achieved by sampling the configuration space,and its physical meaning is the size of the attraction basin corresponding to the local minimums in the potential energy surface.This thesis focuses on two-dimensional carbon allotrope(i.e.graphene-like structure),and the frequency of occurrence is determined in three steps: first,using a topology-based generator to generate 6840 random planar structures,then using density functional theory calculations to relax these structures,and finally,by merging the same structures,1662 different allotropes are found,and allotropes with high frequencies of occurrence can be identified.By plotting the relationship between the frequency of occurrence and the enthalpy of formation,two allotropes that have not been synthesized yet,T-graphene and OP graphene-Z,are proposed.By comparing their formation enthalpy with that of 2D amorphous graphene,it was found that OPG-Z has a higher possibility of synthesis according to the recently proposed synthesizable criterion.The relationship between the frequency of occurrence and the structural geometry is also analyzed.It is found that the frequency of occurrence has a strong dependence on the planar carbon density and average carbon-carbon bond length,but little dependence on the space group and average coordination number.By comparing these planar structure features with the results of a single-atom structure sampling,we show that the rules found in low-dimensional configurational space may provide some guidance when exploring high-dimensional space.Our results provide some inspiration for the synthesis direction of graphene-like planar allotropes.