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The electronic and phononic properties of V2AlC have been extensively studied using ab initio pseudopotential density functional theory. Our investigations revealed that the longest V-V bond and its least variations have led to the stiffer c axis. The nearly unchanged net charge of the C atom under pressure has led to nearly unchanged overlapped populations along the C-V bond. The obvious charge transfer of V → Al has induced significant variations of the overlapped populations along Al-V and V-V bonds. An anomalous variation of charge transfer between V and Al atoms and V-V bond populations at about 700 GPa has been revealed, which may relate to its structural instability at about 731 GPa. Previously calculated structural instability at about 731 GPa has been successfully confirmed by the present phonon dispersion curve. The bonding natures are also studied by the electron density difference, electron density of states, and the energy band structure. [ABSTRACT FROM AUTHOR]

The systematic trends of electronic structure and optical properties of RuO2 consisting of its four phases have been studied by using norm-conserving pseudopotential within the generalized gradient approximation for the exchange-correlation potential. The total density of states (DOS) and energy band structure investigations revealed that the fluorite phase possesses the broadest conduction bandwidth (0-30 eV) and the pyrite phase possesses the narrowest conduction bandwidth (0-5 eV). Study on partial DOS we found that O 2p electrons of the fluorite phase present a significant shift towards the Fermi level and Ru s and p electrons of the rutile phase contribute little to the orbital energy level formation. For the first time, we found that the norm-conserving pseudopotential failed to obtain the normal DOS and energy band distributions for a rutile Ru atom below about -40 eV, whereas such missing electronic distributions could be obtained successfully using an ultrasoft pseudo potential. Investigations on the optical properties further found that the rutile and CaCl2-type phases behave more similarly and the fluorite phase shows the most sensitive response in the whole radiation reaction region. The electron energy loss function revealed that the pyrite phase corresponds to the least relative intensity. [ABSTRACT FROM AUTHOR]