Shell-model description of E1 excitation*

We discuss a microscopic description of E1 excitations based on shell-model calculations. We performed large-scale shell-model calculations for Ca isotopes with Lanczos-strength-function method and $sd$-$pf$-$sdg$ model space allowing up to 3$\hbar\omega$ excitation and obtained their photoabsorption cross sections. It gives a very good description of giant dipole and low-lying pygmy resonances rather independently of smoothing parameter. We also present the feasiblity of the Monte Carlo shell model (MCSM) to study the E1 excitation in order to to treat larger model space. By using the MCSM we discuss some results about light nuclei.