Covalent Radii and New Applications

Ionocovalency theory is defined “…everything exists in ionocovalency, the harmony of ionic energy with the covalent environment.” The authors have succeeded in thoroughly studying ionic energy part of the ionocovalent theory, and will now focus target on the covalent environment part of the theory. The essence of chemical reactions and chemical bonds is the overlap of atomic orbitals, the electron density or the ionocovalent potential. The covalent radius rc is the unique parameter that can be considered as an atomic property derived from molecules for data reduction and can be assigned to the atoms interacting in molecules. In the present study, A new application view of covalent radii of multidimensional world is revealed by the ionocovalency theory which can quantitatively describe the chemical phenomena and qualitatively correlates to the universal observations.

Exploration of Parameters of Ashcroft’s Potential Using Monovacancy Formation Energy and Different Exchange and Correlation Functions for some Trivalent FCC Metals

A pseudopotential approach has been used to study the variation of the vacancy formation energy as a function of the parameter of Ashcroft's empty core model potential (AECMP) and nine different exchange and correlation functions (ECF) for some trivalent fcc metals, viz. Al, La, Sc, γ-Ce, Pr and Yb. The criterion used is that should be greater than the Bohr radius ( ). There is a systematic increase in the fitted value of in going from one ECF to another, as follows: KK < Sham < GV < Kle < Harr < VS < Tay < Hub < MD and it is difficult to assign a particular value of for all ECFs for a particular trivalent fcc metal. The inherent simplicity of AECMP makes it difficult to have a universal parameter for all types of atomic property calculations.

Formation of Point Defects in Dilute FCC Alloys

Using pseudopotential approach, vacancy formation energy , different non-split interstitial formation energies and binding energy for the vacancy-impurity pair and that for interstitial impurity over host have been calculated in some cubic fcc metal systems, viz. copper, silver, gold and lead using Ashcroft's potential and Taylor's exchange and correlation function with standard (AT) and fitted to (ATF) and also Heine-Abarenkov’s model potential and same exchange and correlations (HAT). It is difficult to have a universal value for all types of atomic property calculations. The results show that ATF and HAT combinations are better in comparison to AT. Also, the substitutional impurity adjacent to a vacancy is found to be more loosely bound than the interstitial impurity in fcc metals.