Dimers geometry optimization

As in the case of ArHF, the uncorrected first increases and then decreases when the basis set is improved from aug-cc-pVDZ to aug-cc-pVQZ. The corrected results converge much more regularly. Similar patterns have been observed for other systems as well, including FfH O) and ci (H20) (Xantheas, 1996). The posthoc counterpoise-corrected D s are very close to the results obtained by optimizing the dimer geometry on the counterpoise-corrected surface only for the aug-cc-pVDZ set is the result significantly different. This is due to the fact that the uncorrected F-F distances are too short, an effect that is largest for the aug-cc-pVDZ set. 

This is not associated with a particular method, like HF or Cl, but rather is a basis set problem. Consider what happens when we compare the energy of the hydrogen-bonded water dimer with that of two noninteracting water molecules. Here is the result of an MP2(fc)/6-31G calculation both structures were geometry-optimized, and the energies are corrected for ZPE ... 

In order to assert the charge localization on the termini of the oFLs, semi-empirical calculations have been employed on the positively charged ofi go(fluorene) dimer, trimer and pentamer. The geometry-optimized structures (AMI [4]) have been investigated in their neutral and positively-charged states. Figure 8.5 represents the... 

When the geometry is optimized, predict a regular ground state. The lowest energy is obtained for a non-dimerized geometry r = r2 = 1.40 A. Meanwhile the M = 4 NSBA yield an alternate geometry (see, for instance, Table 2) with interatomic distances that compare very well with the experimental values [46,47]. The study of the energy surface E(ri,r2) or E(r,5), with... 

RVB ansatz The P = 4 infinite-range RVB ansatz of Eq. (57) has been used (see Ref. 34) to obtain the energy as a function of the interatomic distances, ri and r2, and the variational parameters. Upon optimization, this ansatz yields better energy evaluation for the distorted region (see, for instance, Table 2). Furthermore, the RVB ansatz already yields lower energy than the NSBA even when applied to the regular chain, as reported in Table 4. Thus, one always obtains a reasonable estimate of the dimerized geometry. 

An adsorption of silver dimer on a rutile (110) surface has been studied using a DFT model within both cluster and periodic approaches. The calculations show that the interaction of silver dimers can occur both with bridging chain of oxygen atoms or with atoms located in the hollows between chains. The bonding of Ag2 in the hollow is characterized by the positive adsorption energy according to the periodic model. On the other hand, the geometry optimization of similar structures within the cluster model leads to desorption or dissociation of silver dimer. The periodic model is shown more appropriate for this system. 

In Table 4 we present results from the calculation on the neon dimer. The equilibrium distance of the potential is not determined in this work. But based on previous experience with extended geminal models, say on the He2 dimer [45] and the Be2 dimer [47], we can safely assume that the equilibrium distance obtained by a geometry optimization, is close to the experimental value. Hence, the quantity —U (R = 5.84 au), where U(R) is the interatomic... 

A full ab initio calculation is, in principle, capable of including all forces that determine the equilibrium geometry of an H-bond in a balanced manner and can thereby produce a refined picture of the equilibrium geometry. Yet the proper balance is highly dependent on a judicious choice of basis set. A poor selection will produce an imbalance between the components, and the resulting structure may be no better than that obtainable by a crude model at a fraction of the expense. Table 1 compiles for illustrative purposes the geometry optimizations of the water dimer calculated by Frisch et al. with a number of different... 

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