We present Quantum Monte-Carlo results for various positron-electron systems. We discuss the energetics of the bound state of a positronium (Ps) with finite atomic systems: a massive point charge Z, hydrogen (H) and lithium (Li). We also analyze the screening cloud around the positron in the positronium hydride flips) and in the homogeneous electron gas in order to determine the positron annihi...

Recently INTEGRAL/SPI has observed a strong and extended emission resulting from electron-positron annihilation in the Galactic center region, consistent with the Galactic bulge geometry. The positron production rate, estimated to more than 10 per second, is very high and raises a challenging question about the nature of the Galactic positron source. Commonly considered astrophysical positron i...

Positron annihilation spectroscopy is often used to analyze the local electronic structure of materials of technological interest. Reliable theoretical tools are crucial to interpret the measured spectra. Here, we propose a parameter-free gradient correction scheme for a local-density approximation obtained from high-quality quantum Monte Carlo data. The results of our calculations compare favo...