CALCULATION OF RESONANCES IN NEAR-EDGE X-RAY-ABSORPTION FINE-STRUCTURE SPECTRA USING THE CONSTANT CHEMICAL-POTENTIAL LOCAL-DENSITY APPROXIMATION METHOD

Known prescriptions for the implementation of exchange and correlation potentials fail to reproduce the near-edge X-ray absorption fine stru cture (NEXAFS) spectrum for a test case of a gas-phase acetylene molec ule using computer simulations. A new constant chemical potential-loca l density approximation (CCP-LDA) calculation method has been develope d which ensures the constancy of the chemical potential throughout the molecule for which the calculation is performed within the framework of the local density approximation. A Hedin-Lundqvist potential is use d to represent the exchange and correlation potential of the excited s tate. This method provides excellent agreement between theory and expe riment for a range of small gas-phase molecules including acetylene, c arbon monoxide, nitrogen and oxygen.