关于Yan Alexander Wang教授学术报告的通知

报告题目：Chemical Potential, Density Functionals, Nanosystems, and Reaction Mechanisms报告人： Yan Alexander Wang教授 报告时间：2007年5月10日下午14:00-15:30报告地点: 浙江大学玉泉校区教八-107Yan Alexander Wang教授简介: 加拿大British Columbia 大学教授Journal of Computational and Theoretical Nanoscience 编委第六届加拿大计算化学会议主席欢迎广大师生踊跃参加！ 浙江大学化学系附Abstract of “Chemical Potential”The “exchange-correlation derivative discontinuity” has drawn quite considerable attention recently and many research groups have been designing new exchange-correlation density functionals and potentials based on such theoretical results. The backbone of the “exchange-correlation derivative discontinuity” arguments heavily relies on a particular value of the chemical potential, μ = − (I+A)/2, which is the negative of Mulliken’s electronegativity. Here, I and A are the first ionization potential and the first electron affinity of a bounded quantum system under investigation, respectively. Unfortunately, there are already at least six different values of the chemical potential within the present DFT framework. Naturally, one would like to ask the following questions: Which one is the exact value of the chemical potential? Does the exact value of the chemical potential differ from the one commonly employed in the theory of the “exchange-correlation derivative discontinuity”? What are the consequences if they are indeed distinct? To gain an understanding of these issues, we will go through a theoretical journey in search of the correct definition of the functional derivative of the universal density functional in Fock space, which yields the correct definition of the chemical potential at an integer number of electrons [1]. As a consequence, we provide a mathematically rigorous confirmation for the “derivative discontinuity” initially discovered by Perdew et al. [Phys. Rev. Lett. 49, 1691 (1982)]. However, the functional derivative of the exchange-correlation functional is continuous with respect to the number of electrons in Fock space, i.e. there is no “derivative discontinuity” of the exchange-correlation functional at an integer number of electrons. For any external potential converging to the same constant at infinity in all directions, we find that the exact value of the chemical potential at an integer number of electrons is the negative of the first ionization potential, μ = −I, not the popular preference of the negative of Mulliken’s electronegativity.[1] F. E. Zahariev and Y. A. Wang, Phys. Rev. A 70, 042503 (2004).Abstract of “Density Functionals”Density functional theory (DFT) has been firmly established as one of the most widely used first-principles quantum mechanical methods in many fields. Each of the two ways of solving the DFT problem, i.e., the traditional orbital-based Kohn-Sham (KS) and the orbital-free (OF) [1] schemes, has its own strengths and weaknesses. We have developed a new implementation of DFT, namely orbital-corrected OF-DFT (OO-DFT) [2], which coalesces the advantages and avoids the drawbacks of OF-DFT and KS-DFT and allows systems within different chemical bonding environment to be studied at a much lower cost than the traditional self-consistent KS-DFT method. For the cubic-diamond Si and the face-centered-cubic Ag systems, OO-DFT accomplishes the accuracy comparable to fully self-consistent KS-DFT with at most two non-self-consistent iterations. Furthermore, OO-DFT can achieve linear scaling by employing currently available linear-scaling KS-DFT algorithms and may provide a powerful tool to treat large systems of thousands of atoms within different chemical bonding environment much more efficiently than other currently available linear-scaling DFT methods. Our work also provides a new impetus to further improve OF-DFT method currently available in the literature.[1] Y. A. Wang and E. A. Carter, in Theoretical Methods in Condensed Phase Chemistry, edited by S. D. Schwartz (Kluwer, Dordrecht, 2000), p. 117.[2] B.-J. Zhou and Y. A. Wang, J. Chem. Phys. 124, 081107 (2006). (Communication)Abstract of “Nanosystems”The state of the art of creating single-vacancy defected and substitutionally doped single-walled carbon nanotubes (SWCNT’s) has been done with “brutal” physical means under very high temperature of hundreds and thousands of degrees. Such extreme thermal treatments generally do not have a great degree of control over the positions of doping and substitution. Through employing density-functional theory, we will demonstrate the first example of synthesising substitutionally doped SWCNT via chemistry under normal conditions [1-3]. [1] Electronic Properties and Reactivity of Doped and Defected Single-Walled Carbon Nanotubes, W. Q. Tian, L. V. Liu, and Y. A. Wang, in Handbook of Theoretical and Computational Nanotechnology, edited by M. Rieth and W. Schommers (American Scientific, Valencia, California, USA, 2006).[2] Chemical Reaction of Nitric Oxides with the 5-1DB Defect of the Single-Walled Carbon Nanotube, L. V. Liu, W. Q. Tian, and Y. A. Wang, J. Phys. Chem. B 110, 1999-2005 (2006).[3] Electronic Structure and Reactivities of the Perfect, Defected, and Doped Single-Walled Carbon Nanotubes, W. Q. Tian, L. V. Liu, Y.-K. Chen, and Y. A. Wang, J. Comput. Theor. Nanosci. 4, in press (2007). (Invited Review Article)Abstract of “Reaction Mechanisms”The Staudinger reactions of substituted phosphanes and azides have been investigated by using density functional theory. Four different initial reaction mechanisms have been found. All systems studied go through a cis-transition state rather than a trans-transition state or a one-step transition state. Depending on the substituents on the azide and the phosphane, the reaction mechanism with the lowest initial reaction barrier can be classified into three categories: (1) like the parent reaction, PH3 + N3H, the reaction goes through a cis-transition state, approaches a cis-intermediate, overcomes a PN-bond-shifting transition state, reaches a four-membered ring intermediate, dissociates N2 by overcoming a small barrier, and results to the final products: N2 and a phosphazene; (2) once reaching the cis-intermediate, the reaction goes through the N2 eliminating transition state and produces the final products; (3) the reaction has a concerted initial cis-transition state, in which the phosphorus atom attacks the first and the third nitrogen atoms of the azide simultaneously and reaches an intermediate, then the reaction goes through similar steps of the first reaction mechanism. The preference of the initial cis-transition state reaction pathway is thoroughly discussed. The relative stability of the cis- and the trans-intermediates is explored and analyzed with the aid of molecular orbitals. To understand the dynamical aspects of the parent Staudinger reaction, we performed a series of ab initio molecular dynamical simulations from various stationary points on the reaction potential surface, using the Atom-centered Density Matrix Propagation (ADMP) approach. At room temperature, the reaction pathway with the cis-initial attack dominates the parent Staudinger reaction. The driving forces for the reaction are the PH vibration and PH3 subunit rotation during the reaction course.[1] Mechanisms of Staudinger Reactions within Density Functional Theory, W. Q. Tian and Y. A. Wang, J. Org. Chem. 69, 4299-4308 (2004).[2] Dynamics of the Staudinger Reaction, W. Q. Tian and Y. A. Wang, J. Chem. Theory Comput. 1, 353-362 (2005).