The electron density of the environment (ρB) generates the orbital-free embedding potential [Wesolowski and Warshel, J. Phys. Chem., 97 (1993) 8050]. The analytic form of this potential is not known. In practical calculations it is approximated using explicit explicit density-dependent functionals for its exchange-correlation and non-additive kinetic energy components.
Currently, we use the approximation for the kinetic energy component chosen based on our dedicated analyses of different approximations [Wesolowski, J. Chem. Phys. , 107 (1997) 8616].
Atoms representing the system of interest (ρA)
(M+...CO)
and its frozen environment (ρB)
are highlighted in the picture.
Geometry minimization and harmonic frequency calculations for embedded and free M+...CO were performed to obtain the shifts of harmonic frequencies induced by the interactions with the framework of the zeolite.
Table: CO stretching frequency shifts (in cm-1)
| Li+ | Na+ | K+ | |
| M+...CO isolated (model) | 110 | 89 | 74 |
| M+...CO in zeolite (model) | 46 | 38 | 17 |
| M+...CO in zeolite (exp) | 45 | 29-35 | 10-23 |