This paper reports a first-principles study of the crystal structure, chemical bonding, and vibrational spectra of bradleyite, Na3Mg(PO4)(CO3), under pressure. The basis of a linear combination of atomic orbitals and the PBE and PBEsol gradient functionals of the CRYSTAL software code were used. Satisfactory agreement between the calculated and measured lattice parameters was observed. The mechanisms of chemical bond formation were studied using the Mulliken atomic charges and bond overlap populations. The parameters of the Birch–Murnaghan equation of state were determined, and the obtained bulk modulus was used to calculate the Grüneisen mode parameters characterizing the pressure dependence of the infrared absorption and Raman spectra. Bands characteristic of vibrations of the CO3 and PO4 molecular groups with a pronounced contribution from individual groups of oxygen atoms were distinguished in the spectra. The possibility of the existence of Na3Zn(PO4)(CO3) and Na3Pb(PO4)(CO3) crystals with the bradleyite structure was shown.
Yu. N. Zhuravlev (Thu,) studied this question.