Linear Scaling High-spin Open-shell LocalCorrelation MethodsVon der Fakultät Chemie der Universität Stuttgartzur Erlangung der Würde eines Doktors derNaturwissenschaften (Dr. rer. nat.) genehmigte Abhandlungvorgelegt vonYu Liuaus DalianHauptberichter: Prof. Dr. H.-J. Werner, Universität StuttgartMitberichter: Prof. Dr. G. Rauhut, Universität StuttgartTag der mündlichen Prüfung: 15 March 2011Institut für Theoretische Chemie der Universität Stuttgart2011AcknowledgmentsFirst, I would like to thank my parents, and specially, I give my best thanks to mygrandfather. In the 1940s, he was also astudent who studied chemistry. He believedthat the best place to learn chemistry in the word is Germany. He really dreamedabout getting a PhD in Germany. Unfortunately, due to the second world war, itwas impossible. Four years ago, he sent me to Germany to continue his dream.Unfortunately, he could not wait for me to bring the degree back. However, I reallywish that my grandfather can finish this dream now. I believe that this PhD is alsobelonging to him. ......of course, I also thankmy grandmother, who is lonely waitingfor me to be back.I give my thanks to all the friends from the Stuttgart group, especially FrauRosenkranz who took care of all the complicated administration works. I give mythanks to Aron Bona and Judith Rommel for their works in the application partof this thesis.