Evaluating the Curie-Weiss Temperature of a Magnetic System Composed of Nonequivalent Magnetic Ions in Terms of Spin Exchange Constants

Lee, Kee Hag,Lee, Ji Young,Lee, Changhoon,Whangbo, Myung-Hwan Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.5

Single Organic Molecules Designed as Nanoscale Connectors: Fullerene Isoxazoline Derivatives

Lee, Han-Myong,Lee, Chang-Hoon,Cho, Min-Sil,Hwang, Yong-Gyoo,Lee, Kee-Hag Korean Chemical Society 2004 Bulletin of the Korean Chemical Society Vol.25 No.12

Recently a fullerene isoxazoline was reported as an example for nanoscale connectors in molecular electronic devices. The construction of nanoscale devices is a potentially important area of technology. By using the semiempirical PM3 calculation, we optimized the structures for two fullerene isoxazoline derivatives and thirteen regioisomers of the second addition of a nitride oxide to a fullerene isoxazoline derivative. Our results suggest that fullerene isoxazoline derivatives could be used as nanoscale connectors with the possibility of attaching of spacer units in a specific angle arrangement.

Geometrical and Electronic Characteristics of Au<i>_n</i>O₂^– (<i>n</i> = 2–7)

Lee, Han Myoung,Lee, Kee Hag,Lee, Geunsik,Kim, Kwang S. American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.25

<P>Most density functionals do not properly describe the characteristics of superoxide (O<SUB>2</SUB><SUP>–</SUP>) (i.e., first two vertical electron detachment energies and the excitation energies of neutralized singlet state) of small even-numbered Au<I><SUB>n</SUB></I>O<SUB>2</SUB><SUP>–</SUP> clusters. However, the second-order Møller–Plesset theory (MP2) shows significant charge transfer from Au cluster anions to oxygen molecule and so provides proper electronic characteristics of superoxide of small even-numbered Au<I><SUB>n</SUB></I>O<SUB>2</SUB><SUP>–</SUP> clusters. This has allowed us to properly describe the properties of even-numbered Au<I><SUB>n</SUB></I>O<SUB>2</SUB><SUP>–</SUP> clusters. Even in the case of odd-numbered Au<I><SUB>n</SUB></I>O<SUB>2</SUB><SUP>–</SUP> clusters, we find that Au<SUB>5</SUB><SUP>–</SUP> is a chemically O<SUB>2</SUB>-adsorbed singlet state at 0 K, against a commonly accepted physisorbed triplet state. This is further evidenced by our extensive coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] calculations, including the relativistic effect. However, the entropy effect makes the physisorbed triplet state more stable than the chemisorbed singlet state at higher temperatures, consistent with the experiment. The weak O<SUB>2</SUB> binding by odd-numbered cluster anions (<I>n</I> = 3, 5, and 7) could be further weakened by the entropic effect, which results in van der Waals complexes at high temperatures. The present study reports the geometrical and electronic characteristics of small Au<I><SUB>n</SUB></I>O<SUB>2</SUB><SUP>–</SUP> (<I>n</I> = 2–7) clusters including isomers, which match the corresponding photoelectron spectra (PES).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-25/acs.jpcc.5b03051/production/images/medium/jp-2015-03051a_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b03051'>ACS Electronic Supporting Info</A></P>

MO Calculation of Chlorine Doping Effect on the Y-Ba-Cu-O Superconductor

Lee, Wang Ro,Lee, Kee Hag 圓光大學校 基礎自然科學硏究所 1993 基礎科學硏究誌 Vol.12 No.1

YBa_2Cu_3O_7Cl_z(z=0, 0.5, 1) 형태의 Y-Ba-Cu-O 초전도계에 대하여 Extended Hu¨ckel 분자궤도계산을 점전하를 고려하여 수행하였다. 염소화된 Y-Ba-Cu-O초전도체의 전자구조와 성질을 연구하기 위하여 전체 에너지, 상대적 안정도, Cu(1)의 d_z2-y2 상태와 Cu(2)의 d_x2-y2 상태 사이의 에너지 차이 등을 조사하였다. HOMO-LUMO 에너지 차이와 상대적인 안정도의 관점에서 Y-Ba-Cu-O 초전도계의 high-T_c와 초전도에 YBa_2Cu_3O_7Cl_0.5의 경우가 YBa_2Cu_3O_7Cl의 경우보다 영향을 덜 미칠 것으로 기대되고 점전하를 고려할 때 YBa_2Cu_3O_7Cl의 상대적 안정성이 매우 작아진다.

MO Analysis for the Size Convergence of Model Clusters Relating to High-T_c Superconductor YBa_2Cu_3O_7-X

Lee, Wang Ro,Lee, Kee Hag 圓光大學校 基礎自然科學硏究所 1993 基礎科學硏究誌 Vol.12 No.1

YBCO 고온 초전도체에서 전하 모델 덩어리의 크기에 대한 효과와 CuO_3 사슬의 역할을 이론적으로 설명하기 위해 여러 전하 모델에 대해 extended Hu¨ckel 계산을 하였다. 사용한 전하 모델은 YBa_2Cu_3O_7 고온 초전도체의 Cu_6O_21^28-, Cu_6O_22^30-, Cu_9O_30^39-, Cu_9O_32^43-, Cu_12O_38^48-, Cu_15O_50^65-, Cu_18O_54^66-, Cu_18O_55^68-, Cu_24O_70^84-, Cu_27O_78^93-, Cu_75O_200^225-, Cu_147O_378^413-와 YBa_2Cu_3O_6 절연체의 Cu_6O_18^22-, Cu_9O_26^31-, Cu_12O_32^36-, Cu_15O_42^49-, Cu_18O_46^50-, Cu_24O_60^64-, Cu_27O_66^69-이다. YBa_2Cu_3O_7 고온 초전도체의 전자 구조와 성질을 전하모델 덩어리의 크기에 매우 민감한 변화를 보인 반면 YBa_2Cu_3O_6 절연체는 변화가 매우 단조로움을 볼 수 있다. YBa_2Cu_3O_7 고온 초전도체에서 b축 방향에 따라 있는 CuO_3 사슬이 CuO_2 층간의 상호작용과 전도, 초전도 과정에 중요한 어떤 역할을 하는 것으로 보여진다.

MO Reinvestigation of Fluorine Doping Effect on the Y-Ba-Cu-O Superconductor

Lee, Wang Ro,Lee, Kee Hag 圓光大學校 基礎自然科學硏究所 1993 基礎科學硏究誌 Vol.12 No.1

YBa_2Cu_3O_7F_z(z=0, 0.5, 1) 형태의 Y-Ba-Cu-O 초전도계에 대하여 Extended Hu¨ckel 분자궤도계산을 점전하를 고려하여 수행하였다. 불소화된 Y-Ba-Cu-O 초전도체의 전자구조와 성질을 연구하기 위하여 전체 에너지, 상대적 안정도, Cu(1)의 dx2-y2 상태와 Cu(2)의 dx2-y2상태 사이의 에너지 차이 등을 조사하였다. HOMO-LUMO 에너지 차이와 상대적인 안정도의 관점에서 Y-Ba-Cu-O 초전도계의 high-Tc와 초전도계에 YBa_2Cu_3O_7F_0.5의 경우가 YBa_2Cu_3O_7F보다 영향을 덜 미칠 것으로 점전하를 고려한 경우와 고려하지 않은 경우에 동일하게 예측된다.

Structure and Energetics of (C₆₀)₂²⁺ Conformers: Quantum Chemical Studies

Lee, Chang-Hoon,Park, Sung-Soo,Lee, Wang-Ro,Lee, Kee-Hag Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.2

The geometrical structures and energetics of positively doubly charged fullerene dimer $(C_{60})_2{^{2+}}$ conformers were studied using semiempirical PM3 and MNDO, Hartree-Fock (HF), and Hybrid B3LYP density functional methods. The shape of the HOMO-LUMO for the three conformers was also analyzed. The gauche conformer was the most stable of the three conformers. The anti conformer was more stable than the syn conformer.

Bond and Electronic Structure of the C60+ Cation

Park. TY,Lee, Wang Ro,Chon, Hee Cha,Lee, Han Myoung,Lee, Kee Hag 圓光大學校 1996 論文集 Vol.31 No.2

Modified Su-Schriffer-Heeger (SSH) model Hamiltonian 을 이용하여 이온화에 의한 ??의 전자구조 및 분자구조에 대한 효과를 연구하였다. ?? 대칭의 중성 ?? 이 이온화되어 +1 의 하전을 갖게되면 결합구조는 electron-phonon coupling 세기에 따라 ??, C₁및 C₂의 대칭으로 변형된다. ?? 양이온의 ground state 에 대한 전자구조에 대한 약한 electron-phonon coupling 영역에서는 Jahn-Teller distortion 이 나타난다. 반면에 중간세기의 electron-phonon coupling 영역에서는 self-delocalized states 가 얻어지고 강한 electron-phonon coupling 영역에서는 다시 delocalized electronic states 가 얻어졌다. The effects caused by the ionization on the electronic structure and geometry on ?? are studied by the modified Su-Schriffer-Heeger (SSH) model Hamiltonian. After the ionization of ??, the bond structure of the singly charged ?? cation is deformed from ?? symmetry of the neutral ?? to ??, C₁and C₂, which is dependent upon the change of the electron-phonon coupling strength. The electronic structure of the ?? cation ground state undergoes Jahn-Teller distortion in the weak electron-phonon coupling region, while self-localized states occur in the intermediate electron-phonon region, but delocalized electronic states appear again in the strong electron-phonon region.

Frontier Orbitals of Fifteen C₂₀H₁₇(OH)₃ Regioisomers: Hybrid DFT B3LYP Study

Lee, Seol,Lee, Ji Young,Lee, Kee Hag Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.8

The hybrid density-functional (B3LYP/6-31G(d,p)) method was used to analyze the substitution effect on the $C_{20}H_{20}$ cage based on calculation of the frontier orbitals of fifteen $C_{20}H_{17}(OH)_3$ derivatives. All substitution products were geometrically optimized without constraints and confirmed by frequency analysis. The results suggest that the cis-1 cis-1 cis-2 regioisomer is the most stable isomer, which implies that hydrogen bonding exerts a stronger effect on the relative energies of the trihydroxide than long-range interactions. Thus, this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest. While the LUMO of each of the $C_{20}H_{17}(OH)_3$ regioisomers was equivalently delocalized over the void within the cage, the HOMO was limitedly delocalized on substituents and carbons in close proximity to the substituents. The characteristics of the HOMO of each of the regioisomers vary based on the substitution sites. This indicates that the 15 regioisomers of each $C_{20}H_{20}$ trisubstituted derivative might undergo an entirely different set of characteristic chemical reactions with electrophilic reagents. The results further suggest that the penta-substituted OH groups on the surface of the fullerene cage are more likely to be localized on a pentagon than to be homogeneously delocalized.

Full Geometry Optimizations of Bond-Stretch Isomers of C₂₀²⁺ Fullerene Dication by the Hybrid Density Functional B3LYP Methods

Lee, Ji-Hyun,Lee, Chang-Hoon,Park, Sung-S.,Lee, Kee-Hag Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.1

We studied the relative stability and atomic structure of five $C_{20}^{2+}$ isomers obtained by two-electron ionization of a $C_{20}$ cage (the smallest fullerene). All the isomers are bond-stretch isomers, i.e., they differ in bond length. In particular, in one of the isomers with Ih symmetry, all the bond lengths are equal. Full geometry optimizations of the dipositive ion $C_{20}^{2+}$ were performed using the hybrid density functional (B3LYP/6-31G(d)) methods. All isomers were found to be true minima by frequency analysis at the level of B3LYP/6-31G(d) under the reinforced tight convergence criterion and a pruned (99,590) grid. The zero-point correction energy for the cage bond-stretch isomers was in the increasing order $D_{2h}<C_{2h}<C_2<T_h<I_h$ of $C_{20}^{2+}$. The energy difference among the isomers of cage dipositive ions was less than that among neutral cage isomers. Our results suggest that these isomers show bond-stretch isomerism and that they have an identical spin state and an identical potential energy curve. Although the predominant electronic configurations of the isomers are similar, the frontier orbital characteristics are different, implying that we could anticipate an entirely different set of characteristic chemical reactions for each type of HOMO and LUMO.