Material Properties Controlled By Van Der Waals Force:Effects Of Size And Pressure

With the continuous development of the global economy and the advancement of science and technology,human beings are constantly striving not only to improve the quality of life,but also have dream of exploring the unknown world in depth,all of which are inseparable from the understanding and research of materials.The study of intermolecular or non-covalent interactions has always been the key to our understanding of complex molecular systems,especially the binding of molecules in supramolecular systems or condensed states.Van der Waals（vdW）interaction is an important part of the structure,stability and response of many molecular materials,and is critical to understand the actual complex molecular systems for us.They have long-range properties and ubiquity in the molecular system,as measured by the size of the system,and in some cases are strongly nonlinear,affecting the performance of the material at different sizes and pressures.The pairwise addition model of vdW interaction ignores the true many body nature of quantum mechanics between them,while the many body dispersion（MBD）method decomposes the correlation energy into short-range contributions（modeled by semi-local functionals）and long-range contributions（calculated by mapping the complex all-electron problem onto a set of atomic response functions coupled in the dipole approximation）.MBD method systematically improves the binding and cohesive properties,from small molecules to complex supramolecular systems,showing good applicability and offerring the prospect of first-principles modeling of large structurally complex systems with an accurate description of the long-range correlation energy.Based on density functional theory augmented with the many body dispersion interactions（DFT+MBD）,this paper studies the size effect of low-dimensional materials and the pressure effects of high-pressure crystals,exploring the regulation and response of vdW interactions on the geometry and electronic structure of materials.This provides support for understanding the nature of materials and designing materials with the best performance.The specific content is divided into three parts:1.Ultralow stability of gold clusters prohibits the understanding of their intrinsic reactivity（that is vital for revealing the origin of gold’s catalytic properties）.Using DFT+MBD method,we aim to ascertain effective ways in exploiting gold clusters’intrinsic reactivity on carbon nanotubes（CNTs）.We find that the many body van der Waals interactions are essential for gold clusters’reactivity on CNTs and even for O₂activation on these supported clusters.Furthermore,curvature and dopant of CNTs are found to qualitatively change the balance between chemical bond and vdW interaction for gold clusters on CNTs,determining the clusters’morphology,charge states,stability,and reactivity,which rationalize the experimental findings.Remarkably,N doped small curvature CNTs,which effectively stabilize gold clusters and retain their inherent geometric/electronic structures,can be promising candidates for exploiting gold clusters’intrinsic reactivity.2.According to the Mermin–Wagner theorem,ripple deformation is ubiquitous in a two-dimensional（2D）free-standing sheet,influencing the electronic properties.However,the synergistic effects of the unrestricted ripples and the number of layers have still been a topic of extensive debate.To address this issue,we employed DFT+MBD method to investigate the effects of the nondirective ripples on the geometric and electronic structures of multilayered graphene.We found that the many-body effects of vdW forces were essential for the binding of multilayered rippled graphene.The increase of curvature affects the electronic structures of rippled graphene by modifying stacking modes,while the increase in the number of layers can reduce band gap and work function directly.The coupling of these two effects can enhance the chemical activity of rippled graphene.Our results facilitate new insights into the geometric and electronic properties of rippled graphene,which can be generalized to other layered materials.3.High-pressure hydrogen exhibits remarkable phenomena including the insulator-to-metal（IM）transition,however,a complete resolution of its phase diagram is still an elusive goal despite many efforts and much controversy.Theoretical modeling is typically based on DFT with a mean-field description of electronic correlation,which is known rather limited in describing IM transitions.Herein,we show that nonlocal electron correlations play a central role in the relative stability of solid hydrogen phases,and that DFT corrected for these correlations by MBD model reaches the accuracy of quantum Monte-Carlo（QMC）simulations and predicts the same C2/c-24→Cmca-12→Cs（IV）IM transition.In contrast with the conventional assumption that many-body electronic correlations become localized in metallic systems because of exponential screening with interelectronic distance,we find that the anisotropy of electronic response of hydrogen solids under pressure leads to longer-ranged many-body effects in metallic phases relative to insulating ones.This reshapes the understanding of phase diagram of hydrogen solids as well as anisotropic many-body correlations.Then,sulfur trihydride（H₃S）is a theoretically predicted high-pressure superconductor and has been experimentally confirmed to have the highest superconducting transition temperature T_c.Solid H₂S decomposition is considered as the primary source of H₃S,however,it is complex and controversial how H₂S is transformed into H₃S.Herein,we employ DFT augmented with MBD to study a full path of H₂S decomposition at pressure of 20²60 GPa.We find that H₂S starts to decompose into H₃S and other H-S compounds from about 20 GPa,in which the MBD interactions can decrease both the phase transition pressure of H-S compounds and the reaction transition pressure of H₂S decomposition.H₃S₂,H₄S₃,H₃S₅,sulfur and HS₂ are byproducts of H₂S decomposition with increasing pressure.Our results provide a complete phase diagram of H-S compounds during H₂S decomposition,and clarify the pressure range of each product and favoured paths of H₂S decomposition.