The influence of the silicon to aluminum ratio (1, 1.4, and 2) on the site selectivity of cations in faujasite-type zeolite is explained by using calculated atomic net charges and cation-binding energies. The chemical formulae of model compounds are $K_{96}^+Al_{96}Si_{96}O_{384}(1:1)$, $K_{80}^+Al_{80}Si_{112}O_{384}(1.4:1)$, and $K_{64}^+Al_{64}Si_{128}O_{384} (2:1)$. Many experimental results (X-ray data, infrared spectra, and dealumination experiments) suggest that a covalent character is dominant in the zeolite framework. The net charges of framework atoms are derived by using the assumption of equalization of electronegativity in all the atoms. The atomic net charges of hydrogen atoms in fully decationated faujasite-type zeolite ($H_xAl_xSi_{1-x}O_2$) increase with a decrease of the aluminum content. The net charges of aluminum atoms in $K_x^+Al_xSi_{1-x}O_2$ also increase with a decrease of aluminum content. It is easily explained from the calculated atomic net charges that both BrØsnsted acidity and Lewis acidity of the X-type zeolites are less than those of Y-type zeolite. The distribution of cations in model compounds is determined by calculating the binding energies for several possible cases of cation arrangements. Generally, the binding energies of cations decrease with a decrease of the aluminum content. The calculated binding energies indicate that sites I and I' which belong to the same hexagonal prism normally cannot be occupied simultaneously. When the binding energies of cations in sites I and I' are larger than those in sites II and III, the sum of the occupancy factors of sites I and I' is nearly equal to one. The site preference series are obtained as follows: for 1:1 model, I>III'>II>III>I'; for the 1.4:1 model, I>I'>II>III'>III; and for the 2:1 model, I'>I>II>III'>III.
Molecular Orbital Calculation of Several Ices using Pseudo-Lattice Method
Molecular orbital studies of several ices ($I_h$, $I_c$, III, IX, VI) were made using pseudo-lattice method. According to the method water molecules in ice model experience an identical environment without using periodic boundary conditions. It is found that the stability of ice $I_h$ compared to $I_c$ has its origin in the structural difference of the hydrogen bond parallel to c-axis. The difference in binding energy between proton-order and proton-disorder ice $I_h$ is negligible (0.01 kcal/mole), and thus the residual entropy of ice $I_h$ becomes important for determining the proton-orderliness in ice III, the model in which hydrogen atoms are lined on O-O bond is energetically favorable. Linear hydrogen bond models of ice III and ice IX cannot descriminate the stability between ice III and ice IX. In ice VI, a linear hydrogen bond model is considerably unstable because of the repulsive contact of nonhydrogen bonded neighbours. For high pressure ices having distorted hydrogen bonds, the positions of hydrogen atoms play an important role in determining the binding energies and charge distributions of the ices.
제올라이트에 관한 이론적 연구
고전적인 원자 또는 분자간의 인력(classical intermolecular potential energy)을 사용하여 X-, Y-형의 제올라이트에 있어서의 양이온의 위치의 Selectivity와 Aluminum의 양의 변화에 따른 산성도를 electronegativity equalization방법을 사용하여 구하였다.
양이온의 occupancy factor는 X-ray를 잘 설명할 수 있는 결과를 얻었고 또 산성도에 있어서도 지금까지의 실험된 결과들과 잘 일치함을 보여 주었다. 특히 제올라이트의 framework를 공유결합으로 간주하여 얻어진 원자들의 전하량은 이온결합으로 간주하여 얻어진 경우보다 타당함을 알 수 있다.
얼음들에 대한 양자 역학적 계산
CNDO/2를 바탕으로 하여 고체를 설명하기 위하여 만들어진 가상격자방법 (Pseudo-Lattice method)을 사용하여 얻어진 각각 다른 온도와 압력 하에서 나타나는 얼음들의 안정도를 여러 가능한 수소들의 배열에 따라 계산한 결과 격자 에너지는 정성적으로 상도에 나타나는 각 얼음들의 안정도를 잘 설명해 준다.
또 이 Pseudo-Lattice방법을 모든 분자 결정성의 고체에 적용할 수 있는 방법임을 암시해 준다. 얼음에 있어서 고압이 될수록 수소원자들의 배열이 격자 에너지와 전하량에 미치는 영향이 커짐을 알 수 있고 따라서 이들의 정확한 위치의 결정은 매우 중요함을 알 수 있다.
