  Direct studies of intense laser-solid interactions is still of great
challenges, because of the many coupled physical mechanisms, such as direct
laser heating, ionization dynamics, collision among charged particles, and
electrostatic or electromagnetic instabilities, to name just a few. Here, we
present a full particle-in-cell simulation (PIC) framework, which enables us to
calculate laser-solid interactions in a "first principle" way, covering almost
"all" the coupled physical mechanisms. Apart from the mechanisms above, the
numerical self-heating of PIC simulations, which usually appears in
solid-density plasmas, is also well controlled by the proposed
"layered-density" method. This method can be easily implemented into the
state-of-the-art PIC codes. Especially, the electron heating/acceleration at
relativistically intense laser-solid interactions in the presence of large
scale pre-formed plasmas is re-investigated by this PIC code. Results indicate
that collisional damping (even though it is very week) can significantly
influence the electron heating/acceleration in front of the target. Furthermore
the Bremsstrahlung radiation will be enhanced by $2\sim3$ times when the solid
is dramatically heated and ionized. For the considered case, where laser is of
intensity $10^{20}\ \text{W}/\text{cm}^2$ and pre-plasma in front of the solid
target is of scale-length $10\ \mu\text{m}$, collision damping coupled with
ionization dynamics and Bremsstrahlung radiations is shown to lower the
"cut-off" electron energy by $25\%$. In addition, the resistive electromagnetic
fields due to Ohmic-heating also play a non-ignorable role and must be included
in real laser-solid interactions.
