On the performance of the open-shell perturbation theory  

作　　者：CHEN FeiWu WEI MeiJu LIU WenJian 

机构地区：[1]Department of Chemistry, University of Science and Technology Beijing, Beijing 100083, China [2]Beijing National Laboratory for Molecular Sciences, Institute of Theoretical and Computational Chemistry, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

出　　处：《Science China Chemistry》2011年第3期446-453,共8页中国科学（化学英文版）

基　　金：supported by the National Natural Science Foundation of China (20473011, 20773011 and 20625311)

摘　　要：A few open-shell molecules are taken as examples in order to examine the performance of the open-shell perturbation theory for electron correlation(J Chem Theory Comput,2009,5:931–936).The convergence of the perturbation series is shown to be stable for the doublet state of NH2 at both the equilibrium and stretched geometries.The equilibrium bond lengths,and harmonic and anharmonic vibrational frequencies are calculated for NO(X2),OH(X2),CH(X2)and NH(X2)with different second-order perturbation theories at the cc-pVDZ,cc-pVTZ and cc-pVQZ levels.The ground state energies of BeF(X2+), MgH(X2+)and the HCCl triplet state have also been computed with various perturbation theories and compared with configuration interaction with single and double excitations(CISD)and CISD+Davidson correction.The energy difference between the formaldehyde(H2CO + )and hydroxymethylene(HCOH+)radical cations has been computed.Our perturbation theory predicts correctly that H2CO + is more stable than HCOH+.However,calculations using UMP2,CASPT2,the Z-averaged perturbation theory and restricted Mφller–Plesset theory fail even to produce the correct sign of the energy difference.A few open-shell molecules are taken as examples in order to examine the performance of the open-shell perturbation theory for electron correlation（J Chem Theory Comput,2009,5：931–936）.The convergence of the perturbation series is shown to be stable for the doublet state of NH2 at both the equilibrium and stretched geometries.The equilibrium bond lengths,and harmonic and anharmonic vibrational frequencies are calculated for NO（X2）,OH（X2）,CH（X2）and NH（X2）with different second-order perturbation theories at the cc-pVDZ,cc-pVTZ and cc-pVQZ levels.The ground state energies of BeF（X2＋）, MgH（X2＋）and the HCCl triplet state have also been computed with various perturbation theories and compared with configuration interaction with single and double excitations（CISD）and CISD＋Davidson correction.The energy difference between the formaldehyde（H2CO ＋ ）and hydroxymethylene（HCOH＋）radical cations has been computed.Our perturbation theory predicts correctly that H2CO ＋ is more stable than HCOH＋.However,calculations using UMP2,CASPT2,the Z-averaged perturbation theory and restricted Mφller–Plesset theory fail even to produce the correct sign of the energy difference.

关 键 词：open shell perturbation theory CONVERGENCE bond length harmonic vibrational frequency 

分 类 号：O413.1[理学—理论物理] TQ572.1[理学—物理]