Excited electronic state calculations by the transcorrelated variational Monte Carlo method: application to a helium atom

We have implemented the excited electronic state calculations for a helium atom by the transcorrelated variational Monte Carlo (TC-VMC) method. In this method, Jastrow-Slater-type wave function is efficiently optimized not only for the Jastrow factor but also for the Slater determinant. Since the formalism for the TC-VMC method is based on the variance minimization, excited states as well as the ground state calculations are feasible. It is found that both the first and the second excitation energies given by TC-VMC are much closer to the experimental data than those given by the variational Monte Carlo method with using the Hartree-Fock orbitals. The successful results in the TC-VMC method are considered to be due to the nodal optimization of the wave functions.     

Mechanocaloric properties of poly(dimethylsiloxane) and ethylene–propylene rubbers

We measured the temperature change in strips of poly(dimethylsiloxane) (PDMS) and ethylene–propylene rubbers that occurred as they were stretched and allowed to shrink by a factor of 3.5–4.5, along with the tensile force that effected the deformation. Main results obtained are as follows: (1) the temperature change is fully reversible in E–P rubber and slightly but definitely irreversible in PDMS rubber. The temperature rise in the latter on stretching is larger than the fall on shrinking by ca. 20 %. (2) The reversible part of heat that evolves from or is absorbed by PDMS rubber is smaller than, but close to, the mechanical energy expended. For E–P rubber, the heat generated greatly exceeds the expended mechanical energy. (3) The entropy of extension as a function of extension is reproduced well by Wang and Guth calculation for PDMS rubber, but not for E–P rubber.     

Experimental and theoretical studies on thermodynamics and properties of tautomers of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates

Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by ¹H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a/b of dihydropyrimidines (DPs) 1, 2, and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (ΔG), enthalpy differences (ΔH), and entropy differences (ΔS), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs.