Theoretical Study Of Temperature Dependence Research Articles

Theoretical study of temperature dependence and Rayleigh scattering properties of chloride hydration clusters.

Cl(-)(H2O)n (n = 5-6) clusters were investigated using a basin hopping (BH) method coupled with density functional theory (DFT). Structures, energetics, thermodynamics, and vibrational frequencies were obtained using high level ab initio calculations. DF-LMP2 (second-order Møller-Plesset perturbation theory using local and density fitting approximations) with an appropriate basis set were employed for final optimization and frequency calculation, which has been benchmarked in a recent study. The global minimum of Cl(-)(H2O)5 was verified and the new competitive local minimum of Cl(-)(H2O)6 was offered. Considering the increasing complexity of the large system and the high flexibility of the hydrogen bonding environment, Boltzmann averaged Gibbs free energy was provided taking into account the contributions of local minima on the potential energy surface. Finally, the temperature dependence of the conformational population for isomers of Cl(-)(H2O)n (n = 5-6) and Rayleigh scattering properties of Cl(-)(H2O)n (n = 1-6) have been investigated systematically for the first time.

A theoretical study of temperature dependence of cluster formation from sulfuric acid and ammonia

We have performed density functional theory (BL3YP) and ab initio (MP2) calculations to investigate the energetics of the cluster formation for (NH3)m(H2SO4) and (NH3)(H2SO4)n (m,n=1–6) in the atmospherically-relevant temperature range between 200 and 300K. For (NH3)m(H2SO4) clusters, the binding increases from m=1 to 6 at 200K, while the most stable complex at 300K is the cluster with m=2. For (NH3)(H2SO4)n clusters, the binding is more stable for those with larger n. There is a strong temperature dependence for the (NH3)m(H2SO4) cluster formation; the lowest free energy shifts from m=6 at T=200K to m=5 around T=240K and further to m=2 at T⩾280K. The temperature effects on (NH3)(H2SO4)n clusters are much less stronger, while there is still a similar trend which favors larger n in the entire temperature range from 200 to 300K.

The influence of hydrogen bonds on electron transfer rate in photosynthetic RCs

Hydrogen bonds formed between photosynthetic reaction centers (RCs) and their cofactors were shown to affect the efficacy of electron transfer. The mechanism of such influence is determined by sensitivity of hydrogen bonds to electron density rearrangements, which alter hydrogen bonds potential energy surface. Quantum chemistry calculations were carried out on a system consisting of a primary quinone Q A, non-heme Fe 2+ ion and neighboring residues . The primary quinone forms two hydrogen bonds with its environment, one of which was shown to be highly sensitive to the Q A state. In the case of the reduced primary quinone two stable hydrogen bond proton positions were shown to exist on [Q A-His M219] hydrogen bond line, while there is only one stable proton position in the case of the oxidized primary quinone. Taking into account this fact and also the ability of proton to transfer between potential energy wells along a hydrogen bond, theoretical study of temperature dependence of hydrogen bond polarization was carried out. Current theory was successfully applied to interpret dark P +/Q A − recombination rate temperature dependence.

Theoretical study of temperature dependence of spontaneous polarization, optical properties and linear electro-optic coefficients of tetragonal KNbO3

The microscopic mechanisms of refractive indices, birefringence, spontaneous polarization and linear electro-optic effects are examined for KNbO3 using a microscopic model which takes into account a quantum method based upon the orbital approximation and the dipole-dipole interaction due to the local field acting on the constituent ions. It is found that the electronic polarizabilities play a major role in these calculations and that the birefringence n and the linear electro-optic coefficients are in good agreement with the experimental data.

Theoretical study of temperature dependence of spontaneous polarization, optical properties and free and clamped linear electrooptic coefficients of BaTiO3 in the tetragonal phase

The microscopic mechanism of refractive indices, birefringence, spontaneous polarization and free and clamped electrooptic effects of BaTiO3 is discussed by using a microscopic model taking account of a quantum method based upon the orbital approximation and the dipole-dipole interaction due to the local field acting on the constituent ions. It is found that the electronic polarizabilities play a major role in these calculations and that the birefringence δn and the free and clamped linear electrooptic coefficients are in good agreement with the experimental data.