Compton profile and charge transfer of CaCl2

The purpose of the present work study the experimental of electron momentum density for CaCl2 which is measured for the first time by imploying 100mCi 241 Am Compton spectrometer. To compare experimental momentum densities the Compton profiles has been studied using Hartree–Fock within linear combination of atomic orbitals(LCAO) and simple ionic model. The experimental isotropic profiles are found to be relatively in better agreement with the Hartree–Fock data. To evaluate the charge transfer the ionic model for number of configuration of (Ca +x )(Cl -x/2 )2 has been used to estimate the charge transfer on compound formation. This model supports transfer of 0.5 electrons from 4S state of each Ca Atom to 3P State of Cl2.


1.INTRODUCTION
Calcium chloride (CaCl 2 ) a II-VII compound with orthorhombic wurtzite structure space group pnnm, No 58, having a large direct band gap (6.9 eV), many workers have reported theoretical and experimental work on the structural, electronic, elastic, vibrational and pressure-induced properties. For example , Jean-Miche et al. [1] has studied the phase transition sequence induced by high-pressure. ab initio prediction of the potential energy surface and vibration-rotating energy levels of calcium chloride has been reported by Jacek Koput [2], phase transition and optical properties of calcium chloride under high pressure have been calculated using ab intio pseudo potential plane-wave by Lin et al. [3], results show that the transition happens at about 2.9 GPa, which is agreement with experimental data and calculated structure parameters, charge transfers ,bond structure, density of state and optical properties .Valgoma et al. [4] studied the ferroelastic phase transition is CaCl 2 .
Monico et al. [5] has studied the geometry parameters, frequencies, heats of formation and bond dissociation energy in CaCl 2 . Beaden et al. [6] calculate the binding energy of the 3P electrons for Ca ++ in the free atom and find it value is 25.5 eV. Also Sugiura et al. [7] has studied K-shell, x-ray spectra and electronic band structure of alkaline-earth chloride and calculations the band gap of calcium chloride. The common application of the calcium chloride include brine for refrigeration plants, ice dust control on roads and desiccation etc. because of its hygroscopic nature [8]. Due to hygroscopic nature anhydrous calcium chloride must be kept in tightly sealed, air-tight containers.
The purpose of the present paper is many folds

A. HF-LCAO Calculation
The Compton scattering is an inelastic scattering in which an energetic photon collides with an electron and transfers a part of its energy to the electron. This technique has been employed to probe the ground-state electron momentum densities of a variety of materials.
Within impulse approximation (IA), the Compton profile is related to the Doppler broadening of scattered radiations by the motion of electrons in the target [13]. From such experiments, one measures the double differential cross section that is related to Compton profile J(pz) as where n(p) is the ground-state electron momentum density. The momentum density, within an independent-particle model, is given by Eq. To compute the theoretical Compton profile, the HF-LCAO method embodies in CRYSTAL code [15] of Torino group has been used. In this method each crystalline orbital ψ i (r.k) is a linear combination of Bloch functions φ μ (r.k) defined in terms of local function φ μ (r) normally referred as atomic. The local functions are expressed as linear combination of certain number of individually normalized Gaussian type function. For Ca and Cl 2 the local functions were constructed from the Gaussian type basis sets [16]. The HF operator Hamiltonian is defined as, [15].

B. Ionic Model
The theoretical Compton profile of CaCl 2 for different ionic configurations was calculated from the free atom profile of Ca and Cl 2 as taken from Bigge et al. [16].

4.RESULTS AND DISCUSSION
In

CONCLUSIONS
In this paper,Compton profile measurement of polycrystalline CaCl 2 is reported. The experimental data on polycrystalline sample has been compared with the HF-LCAO and simple ionic model calculations are in a good agreement with the measurement. The HF-LCAO based momentum density shows better agreement with the measurement, the ionic model suggests a transfer of 0.5 electrons from 4S state of each Ca atom to 3P state of Cl 2 .
Measurement on single crystalline samples with better resolution and high statistics will be very helpful to examine these finding rigorously.