COSMO COnductor-like Screening effects

COSMO (conductor-like screening model) a method for including solvation effects in orbital-based calculations... 

In addition to these external electric or magnetic field as a perturbation parameter, solvents can be another option. Solvents having different dielectric constants would mimic different field strengths. In the recent past, several solvent models have been used to understand the reactivity of chemical species [55,56]. The well-acclaimed review article on solvent effects can be exploited in this regard [57]. Different solvent models such as conductor-like screening model (COSMO), polarizable continuum model (PCM), effective fragment potential (EFP) model with mostly water as a solvent have been used in the above studies. 

Although many satisfactory VCD studies based on the gas phase simulations have been reported, it may be necessary to account for solvent effects in order to achieve conclusive AC assignments. Currently, there are two approaches to take solvent effects into account. One of them is the implicit solvent model, which treats a solvent as a continuum dielectric environment and does not consider the explicit intermolecular interactions between chiral solute and solvent molecules. The two most used computational methods for the implicit solvent model are the polarizable continuum model (PCM) [93-95] and the conductor-like screening model (COSMO) [96, 97]. In this treatment, geometry optimizations and harmonic frequency calculations are repeated with the inclusion of PCM or COSMO for all the conformers found. Changes in the conformational structures, the relative energies of conformers, and the harmonic frequencies, as well as in the VA and VCD intensities have been reported with the inclusion of the implicit solvent model. The second approach is called the explicit solvent model, which takes the explicit intermolecular interactions into account. The applications of these two approaches, in particular the latter one will be further discussed in Sect. 4.2. 

The conductor-like screening model (COSMO) approach replaces the dielectric medium with a conducting medium (basically a medium that effectively has an infinite dielectric constant). Interlocking spheres are used to generate the cavity. The conductor-like screening has been implemented as a PCM version, called CPCM.128,129... 

Several groups have also made relevant contribution to the evolution of the original PCM. A related model based on conductor-like screening (COSMO) has been developed recently by Klamt and Schuiirmann [13]. Likewise, another approach to the PCM has been proposed in which the cavity surface is determined in terms of an electronic isodensity surface [14]. Olivares del Valle and coworkers [15] have focused their attention on aspects such as the inclusion of correlation effects in the PCM, or on the role of nonadditive effects in solute-solvent interactions. Pascual-Ahuir et al. [16] have paid most attention to the problem of the definition of the cavity surface. The work done in Barcelona has focussed mainly on the parametrization of the PCM to treating aqueous and nonaqueous solvents, as well as the application of the PCM to the study of biochemical systems [17, 18]. Finally, we and others have made new methodological developments to allow the implementation of the PCM in molecular dynamics or in Monte Carlo calculations [19]. 

Onsager s SCRF is the simplest method for taking dielectric medium effects into account and more accurate approaches have been developed such as polarizable continuum modes, " continuum dielectric solvation models, - explicit-solvent dynamic-dielectric screening model, - and conductor-like screening model (COSMO). Extensive refinements of the SCRF method (spherical, elliptical, multicavity models) in conjunction with INDO/CIS were introduced by Zerner and co-workers ° as well. 

Conductor-like Screening Model (COSMO) in reproducing solvent effects... 

Solvent effects may be treated using several models self-consistent reaction field (SCRF) (Karelson et aL 1986, 1993 Kirkwood 1934 Tapia and Goscinski 1975), polarizable continuum model (PCM) (Cammi and Tomasi 1995 Miertui et al. 1981 Tomasi and Persico 1994 Tomasi et al. 2005), surface and simulation of volume polarization for electrostatics (SS(V)PE) (Chipman 1997, 2000, 2002), and conductor-like screening model (COSMO) (Baldridge and Klamt 1997 Klamt 1995 Klamt and Schiiurmann 1993). 

Additionally, for flexible molecules, the presence of multiple conformations may require the consideration of solvent effects, mainly if experimental data in polar solvents are to be reproduced. The relative energies of conformers and their chiroptical properties can be largely affected by solvent effects, and thus, in some cases, the inclusion of either the polarizable continuum model (PCM) or the conductor-like screening model (COSMO) since geometry optimization steps may be beneficial." ... 

---