In the last decade, intense experimental efforts using advanced techniques for sample preparation and characterization have provided a vast quantity of data. These developments have challenged present theoretical understanding and have encouraged the development of theoretical methods interpreting the phenomena observed. Our total energy all‐electron local density theoretical approach, implemented as the full potential linearized augmented plane wave (FLAPW) method, is described and shown to have high precision (to 10−9 in the total energy) and stability for describing the structural, electronic, and magnetic properties of (i) free surfaces [including surface relaxation and reconstruction, e.g., W(001)], (ii) interface phenomena in Au/Cr/Au(001) sandwiches [e.g., prediction of the enhanced magnetic moment on the interface Cr site], (iii) catalytic promotion and poisoning of molecular dissociation on surfaces [e.g., CO + K or S/Ni(001)]. The three examples just cited illustrate the present predictive power...