Comment on "Free energy simulations of single and double ion occupancy in gramicidin A" [J. Chem. Phys. 126, 105103 (2007)

In a recent article published by Bastug and Kuyucak [J. Chem. Phys.126, 105103 (2007)] investigated the microscopic factors affecting double ion occupancy in the gramicidin channel. The analysis relied largely on the one-dimensional potential of mean force of ions along the axis of the channel (the so-called free energy profile of the ion along the channel axis), as well as on the calculation of the equilibrium association constant of the ions in the channel binding sites. It is the purpose of this communication to clarify this issue.     

Comment on "Excitations in photoactive molecules from quantum Monte Carlo" [J. Chem. Phys. 121, 5836 (2004)

It is shown that the qualitative differences between high-level ab initio calculations and restricted open-shell Kohn-Sham (ROKS) results for the lowest singlet excited electronic state of formaldimine along a particular isomerization path found by Schautz, Buda, and Filippi [J. Chem. Phys.121, 5836 (2004)] play a minor role in molecular dynamics simulations of photoisomerization at room temperature. In fact, ROKS yields, within its well-known limitations, a good representation of the physically relevant isomerization pathway.