  We report an {\it ab initio} simulation study of changes in structural and
dynamic properties of liquid Si at 7 pressures ranging from 10.2 GPa to 24.3
GPa along the isothermal line 1150~K, which is above the minimum of the melting
line. The increase of pressure from 10.2 GPa to 16 GPa causes strong reduction
in the tetrahedral ordering of the most close neighbors. The diffusion
coefficient shows a linear decay vs drop in atomic volume, that agrees with
theoretical prediction for simple liquid metals, thus not showing any feature
at the pressures corresponding to the different crystal phase boundaries. The
Fourier-spectra of velocity autocorrelation function shows two-peak structure
at pressures 20 GPa and higher. These characteristic frequencies correspond
well to the peak frequencies of the transverse current spectral function in the
second pseudo-Brillouin zone. Two almost flat branches of short-wavelength
transverse modes were observed for all the studied pressures. We discuss the
pressure evolution of characteristic frequencies in the longitudinal and
transverse branches of collective modes.
