(CdSe)n(n=1,2)团簇性质及CdSe分子热力学性质的理论计算

用密度泛函B3LYP方法、有效核势(ECP)基组LanL2DZ对(CaSe)n(n=1,2)团簇进行了理论研究,得到(CaSe)n(n=1,2)分子体系可能存在的状态及各电子状态的平衡几何Re、谐振频率、偶极矩和离解能De、不同温度、压力下的热力学函数值;设用总能量中的电子和振动能量近似代表CdSe分子处于固态时的能量,用总熵中的电子和振动熵近似代表CdSe分子处于固态时的熵,进而计算了Cd与Se反应的△Hθ、△Sθ、△G,并由此计算出不同温度的反应平衡常数Kp结果表明:在298～1400K温度范围内,Cd与Se反应的自由能值均为负,且随着温度的升高,△Gθ值负的越多,表明在这个温度范围内反应能自发发生,而且自发趋势随温度的升高逐渐增大;平衡常数逐渐减小,即反应进行程度随温度的升高逐渐减小;CdSe分子材料的导电性随压力增大而增强.

Theoretical calculation of structure (CdSe)n(n=1,2)and thermodynamic properties of CdSe

Using density functional method(B3LYP) and LanL2DZ basis sets,the Molecular structure parameters and some thermodynamic functions for(case)n(n=1,2)have been calculated.The calculated results of the molecular ions equilibrium geometry(Re),Vibration Frequency,Dipole moments and Mulliken population and dissociation energy for CdSeX(X=0,+1,+2)are listed in the Table 1,the molecular of Cd2Se2 have four stable structures for singlets states and five stable structures for triplets states.Considering the characteristics of different motion types,the electronic and vibrational energy or entropy of molecule are assumed to be torresponding values of their solid states,then based on this approximation,△Hθ,△Sθ,△Gθ and Kp of reactions for Cd and Se have been calculated.It shows that,with the scope of temperature of 298～1400 K,the value of free reaction of Cd and Se is negative,and the negative value increases with the increasing temperature.,which indieates that within the scope of temperature,the reaction can occur spontaneously,and the tendency of thespontaneity goes up along with the temperature,but the balance constant(Kp) decreases gradually,that is,the degree of the reaction decreases with the increasing temperature.The electric conductivity of the molecule material (CdSe)strengthens with the increasing pressure.