Conductor-like screening model COSMO

The conductor-like screening model (COSMO) is a continuum method designed to be fast and robust. This method uses a simpler, more approximate equation for the electrostatic interaction between the solvent and solute. Line the SMx methods, it is based on a solvent accessible surface. Because of this, COSMO calculations require less CPU time than PCM calculations and are less likely to fail to converge. COSMO can be used with a variety of semiempirical, ah initio, and DFT methods. There is also some loss of accuracy as a result of this approximation. 

In 1995, one of the authors (A.K.) introduced the state of a molecule embedded in a perfect conductor as an alternative reference state, which is almost as clean and simple as the vacuum state. In this state the conductor screens all long-range Coulomb interactions by polarization charges on the molecular interaction surface. Thus, we have a different reference state of noninteracting molecules. This state may be considered as the North Pole of our globe. Due to its computational accessibility by quantum chemical calculations combined with the conductor-like screening model (COSMO) [21] we will denote this as the COSMO state. 

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. 

Conductor-like screening model (COSMO) is one of variants of PCM method [29]. In this method, the cavity is considered to be embedded in a conductor with an infinite dielectric constant [29]. An extension to this method, called COSMO-RS... 

Here, r denotes the position vector of the charges qt with respect to the center of the sphere, and r, the distance from the center. By applying the dielectric scaling function for dipoles (Eq. (2.3)), which—as we have seen in Fig. 2.1—is also a good approximation for most other multipole orders, it was immediately clear that the idea of using a scaled conductor instead of the EDBC leads to a considerable simplification of the mathematics of dielectric continuum solvation models, with very small loss of accuracy. It may also help the finding of closed analytic solutions where at present only multipole expansions are available, as in the case of the spherical cavity. Thus the Conductor-like Screening Model (COSMO) was bom. 

In addition to SMx and the cluster-continuum model, other continuum models have also been used to study reactions in liquids, including the polarized continuum model [133-135] (PCM), the conductor-like screening model (COSMO [136] and COSMO-RS [137,138]), the generalized COSMO [139] (GCOSMO) model, conductorlike PCM [140] (CPCM), and isodensity PCM [141] (IPCM). 

Fig. 9 Nuclear spin-spin coupling constants J(195Pt-205Tl) for complexes I-V (see Fig. 8), from ZORA DFT computations. Data taken from Autschbach and Le Guennic [126]. Different computational models were applied Model A includes explicit water molecules. In Model B, a continuum model (conductor-like screening model, COSMO) is applied in addition to the explicit solvent molecules of model A. Model C differs from model B in that instead of the VWN functional the statistical averaging of orbital potentials (SAOP) XC potential was used, which allows more accurate computations of NMR parameters [32]. The NMR measurements were carried out in aqueous solution [99,130]...

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... 

A modified version, the conductor-like screening model (COSMO), was later proposed by Klamt and Schiiurmann, where the equations above were solved for the continuum being a conductor with g -> oo. Subsequently, the potential was scaled in order to take the finite value of g into account. 

Generalized Bom (GB) approach. The most common implicit models used for small molecules are the Conductor-Like Screening Model (COSMO) [77,78], the DPCM [79], the Conductor-Like Modification to the Polarized Continuum Model (CPCM) [80,81], the Integral Equation Formalism Implementation of PCM (IEF-PCM) [82] PB models, and the GB SMx models of Cramer and Truhlar [23,83-86]. The newest Minnesota solvation models are the SMD universal Solvation Model based on solute electron density [26] and the SMLVE method, which combines the surface and volume polarization for electrostatic interactions model (SVPE) [87-89] with semiempirical terms that account for local electrostatics [90]. Further details on these methods can be found in Chapter 11 of Reference [23]. 

Another approach that is similar to the BE continuum solvation model is the conductor-like screening model (COSMO) [22]. The total electrostatic energy, Ueie, of a cavity with some charges q( inside a conductor is given by the following equation ... 

The Conductor-like Screening Model (COSMO) also uses molecular shaped cavities and represents the electrostatic potential by partial atomic charges (Klamt and Schuurmann [84]). COSMO was initially implemented for semiempirical methods but more recently was also used in conjunction to ab initio methods (Andzelm et al. [85]). 

A method that is very similar to PCM is the conductor-like screening model (COSMO) developed by Klamt and eoworker and used later by Truong and coworkers, and by Barone and Cossi. This model assumes that the surrounding medium is well modeled as a conductor (thus simplifying the eleetrostatics computations) and corrections are made a posteriori for dielectric behavior. 

The conductor-like screening model COSMO), a quantum chemistry-based computational tool integrating biophysical properties such as hydrogen bonding, van der Waals terms, and solvation, was used to characterize the bioisosteric similarity of a set of 6041 analogue pairs extracted from Bioster and of a set of 5823 random pairs from an in-house database [61]. 

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. 

The conductor-like screening model (COSMO) is available for molecules in a solvent. The QM/MM implementation enables treatment of active sites in protein environments with many thousands of atoms. Homogeneous electric fields and point charges can be specified. More advanced environment models are being implemented. 

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