量子化学理论计算英文e1

1、WHAT IS DENSITY FUNCTIONAL THEORY?1.1 EXAMPLES OF DFT IN ACTION1.1.1 1.1.1 Ammonia Synthesis by Heterogeneous Catalysis Ammonia Synthesis by Heterogeneous Catalysis The core reaction in ammonia production is very simple:The core reaction in ammonia production is very simple:NN2 2+3H+3H2 2 2NH 2NH3 3Can a direct connection be made between the shape and Can a direct connection be made between the shape and size of a metal nanoparticle and its activity as a catalyst for size of a metal nanoparticle

2、 and its activity as a catalyst for ammonia synthesis?ammonia synthesis?2Honkala Honkala and and co-workers,co-workers,using using DFT DFT calculations,calculations,showed showed that that the the net net chemical chemical reaction reaction above above proceeds proceeds via via at at least least 12 12 distinct distinct steps steps on on a a metal metal catalyst catalyst and and that that the the rates rates of of these these steps steps depend depend strongly strongly on on the local coordinatio

3、n of the metal atoms that are involved.the local coordination of the metal atoms that are involved.One One of of the the most most important important reactions reactions is is the the breaking breaking of of the the NN2 2 bond bond on on the the catalyst catalyst surface.surface.On On regions regions of of the the catalyst catalyst surface surface that that were were similar similar to to the the surfaces surfaces of of bulk bulk Ru Ru(more(more specispecififically,cally,atomically atomically f

4、lflat at regions),regions),a a great great deal deal of of energy energy is is required required for for this this bond-breaking bond-breaking reactionreaction.31.1.2 1.1.2 Embrittlement of Metals by Trace ImpuritiesEmbrittlement of Metals by Trace ImpuritiesIt It has has been been known known for for over over 100 100 years years that that adding adding tiny tiny amounts amounts of of certain certain impurities impurities to to copper copper can can change change the the metal metal from from b

5、eing being ductile ductile to to a a material material that that will will fracture fracture in in a a brittle brittle way.way.This This occurs,occurs,for for example,example,when when bismuth bismuth(Bi)(Bi)is is present present in in copper(Cu)copper(Cu)at at levels levels below below 100 ppm.100 ppm.Can Can the the changes changes in in copper copper caused caused by by Bi Bi be be explained explained in in a a detailed way?detailed way?4Schweinfest,Schweinfest,Paxton,Paxton,and and Finnis Fi

6、nnis used used DFT DFT calculations calculations to to offer offer a a definitive definitive description description of of how how Bi Bi embrittles embrittles copper.copper.They first used DFT to They first used DFT to predict stressstrain relationshipspredict stressstrain relationshipsfor for pure pure Cu Cu and and Cu Cu containing containing Bi Bi atoms atoms as as impuritiesimpurities.They They explicitly explicitly calculated calculated the the cohesion cohesion energy energy of of a a part

7、icular particular grain grain boundary boundary that that is is known known experimentally experimentally to to be be embrittled by Bi.embrittled by Bi.51.1.3 1.1.3 Materials Properties for Modeling Planetary FormationMaterials Properties for Modeling Planetary FormationThe The extreme extreme conditions conditions that that exist exist inside inside planets planets pose pose some some obvious obvious challenges challenges to to probing probing these these topics topics in in laboratory laborato

8、ry experiments.experiments.DFT DFT calculations calculations can can play play a a useful useful role role in in probing probing material material properties at these extreme conditions.properties at these extreme conditions.6Umemoto et al.wanted to understand what happens to the Umemoto et al.wanted to understand what happens to the structure of MgSiOstructure of MgSiO3 3 at conditions much more extreme than at conditions much more extreme than those found in Earths coremantle boundary.those fo

9、und in Earths coremantle boundary.These calculations predicted that at pressures of 11 Mbar,These calculations predicted that at pressures of 11 Mbar,MgSiOMgSiO3 3 dissociates in the following way:dissociates in the following way:MgSiO3 CaIrO3 structure MgO CsCl structure +SiO2 cotunnite structure.7These These transformations transformations in in the the structures structures of of MgO MgO and and SiOSiO2 2 allow allow an an important important connection connection to to be be made made betwee

10、n between DFT DFT calculations calculations and and experimentsexperiments since since these these transformations transformations occur occur at at conditions conditions that that can can be be directly directly probed probed in in laboratory experiments.laboratory experiments.The The transition transition pressures pressures predicted predicted using using DFT DFT and and observed observed experimentally experimentally are are in in good good agreement,agreement,giving giving a a strong indica

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