Correlated barrier hopping

Figure 8.12. Frequency dependence of the frequency exponent s for various models correlated-barrier hopping (CBH) (WM/kT=75 has been assumed) small polaron (SP), quantum mechanical tunneling (QMT) and overlapping large polaron (OLP)...

In(frequency) curves the value of the exponent is estimated to be 0.9 for the last two cases, which shows a possibility of variable range hopping phenomena [84]. This quantum mechanical tunneling or correlated barrier hopping is based on the pair approximation in which the motion of the carriers is contained within a pair of sites. If the DC and AC conductivities arise from the same hopping mechanism, the pair approximation cannot be applied [85]. Scher and Lax [86] proposed the continuous random network [65]. The frequency-dependent conductivity is given by... 

The molecular dynamics of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) blends was investigated as a function of composition, temperature and frequency using DRS [44]. PVA and CMC were found to be compatible over the range of composition studied. When the dielectric permittivity, loss tangent and a. c. conductivity of all samples were studied as functions of temperature and frequency, the results showed that the dielectric dispersion consisted of both dipolar and interfacial polarization. The frequency dependence of the a.c. conductivity indicated that correlated barrier hopping (CBH) was the most suitable mechanism for conduction. 

Since OH(A Z) is efficiently quenched by N2 via a strongly attractive interaction [174], there is clearly at least one adiabatic surface correlating to OH(A Z) + N2(X i ) that does not have a barrier associated with the final separation of the OHIA Z) and N2(X Z) fragments. Also, there can be only one adiabatic surface for H( S) + N20(X Z ), and this correlates in C, symmetry to OH(X n) + N2(X S), albeit via a substantial barrier that can be traced to an avoided crossing [40]. Thus, access to OH(A i ) + N2(X S) is via a nonadiabatic process, and surface-hopping may be responsible for the observed A Z - X Z chemiluminescence. With complexes, the lack of OH chemiluminescence can be attributed to factors such as (i) specific approach... 

The discrepancy in results between NEB and BV calculations is attributed to correlations between Li and adjacent ions during migration that are neglected in the BV calculation [33]. The electrostatic repulsions between Li and adjacent Fe and B cations and relaxations of the sublattice aroimd the Li ion can be considered in NEB calculations. Therefore, first-principles based on the NEB method are more accurate to calculate the activation barrier for ion hopping in the crystal structure than the BVS method, while the BVS method is an easy and fast computation method to predict possible diffusion pathways. 

---