Articles you may be interested inExcitation energies from extended random phase approximation employed with approximate one-and twoelectron reduced density matrices Communication: Constrained search formulation of the ground state energy as a functional of an idempotent one-matrix J. Chem. Phys. 133, 151102 (2010); 10.1063/1.3505036Systematic construction of approximate one-matrix functionals for the electron-electron repulsion energy A simple extension of the antisymmetrized product of strongly orthogonal geminals theory produces a ''JK-only'' one-matrix functional for the electron-electron repulsion energy of a closed-shell system that is exact for two-electron singlet ground states, size-extensive, and incorporates some intergeminal correlation and thus dispersion effects. The functional is defined only for one-matrices with occupation numbers that can be arranged into sets with elements that sum up to two. Its possible generalizations are discussed.

The primary H/D kinetic isotope effect on the intramolecular proton transfer in malonaldehyde is determined from quantum instanton path integral Monte Carlo simulations on a fully dimensional and validated potential energy surface for temperatures between 250 and 1500 K. Our calculations, based on thermodynamic integration with respect to the mass of the transferring particle, are significantly accelerated by the direct evaluation of the kinetic isotope effect instead of computing it as a ratio of two rate constants. At room temperature, the KIE from the present simulations is 5.2 ± 0.4. The KIE is found to vary considerably as a function of temperature and the low-T behaviour is dominated by the fact that the free energy derivative in the reactant state increases more rapidly than in the transition state. Detailed analysis of the various contributions to the quantum rate constant together with estimates for rates from conventional transition state theory and from periodic orbit theory suggest that the KIE in malonaldehyde is dominated by zero point energy effects and that tunneling plays a minor role at room temperature.