بررسي كوانتومي خواص مكانيكي و توپولوژي چگالي الكتروني بلور و زنجيره هاي اتمي طلا، نقره و مس

چكيده انگليسي :

First principle Study of Mechanical Properties and Topology of Charge Density of Bulk and Mono Atomic Chain of Cu Ag and Au Mohammad Saghayezhian m saghayezhian@ph iut ac ir 2 23 2011 Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language PersianSupervisor Dr S J Hashemifar hashemifar@cc iut ac irAbstractThere are two different view point in mechanical study of materials macroscopic and microscopic Among different methods of studying of mechanical properties of materials first principle methodshave been very successful Quantum mechanical based microscopic description of macroscopic me chanical properties including young s modulus bulk modulus mechanical anisotropy stress straincurves is an attractive issue in theoretical material science In the present effort we tried to shedlight on interconnection of macro and micro mechanical properties our main purpose is to show thatit is possible to find another way of achieving mechanical characteristics In order to perform this taskproperly we computed mechanical properties of widely applied Cu Ag and Au from first principleapproach and then analyzed evolution of charge density which is proven to has a deep connection withmechanical properties i e stress strain and is a microscopic observable In this regard along withincreasing strain in a systematic way the topological characteristics of charge density was monitored We observed that elastic plastic transition in 100 coincides with topological transition of charge den sity while in 111 direction elastic plastic transition has a geometrical character For the first time we realized that the key point in the strain induced evolution of charge density is the important roleof cages charge density minima Further investigation showed that variation of curvature of cagescan locate Yield point and Ultimate Tensile Strength which are two important points on stress straincurves regardless of tensile direction Therefore there would be another method of finding this points i e studying of strain induced charge density evolution Experimental tensile tests on Cu Ag and Au in 111 direction showed that they are capable of forming mono atomic chains Phys Rev B78 115409 Mono atomic chains can be a good candidate for application in nano electronic industry Scientistshope that they could use mono atomic in nano integrated circuits as connectors of nano transistors In order to finding the theoretical parameter for chain ability of Au Ag and Cu we used universalenergy function and topology of charge density to attain more insight into process of elongation tomono atomic chain With the aid of stress strain curves we found that chaining process starts be fore ultimate tensile strength and also we found that critical points of charge density are influentialin chain formation Using above mentioned information we proved that Au is the most promisingmetal for ending up to a mono atomic chain As stated before cage critical points are important inthe process of chain formation and the amount of charge density in them can predict that which metalis capable of elongation to mono atomic chain Further investigation lead us to a new conclusion thatthe cage ring cage angle could provide a good reason for formation of AuAg alloy chain Keywords First principle study Quantum stress Mechanical properties topology of charge density mono atomic chains Au Ag Cu

سقاي ژيان، محمد

بررسي كوانتومي خواص مكانيكي و توپولوژي چگالي الكتروني بلور و زنجيره هاي اتمي طلا، نقره و مس

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