  We study the imaginary-time relaxation critical dynamics of the
Neel-paramagnetic quantum phase transition in the two-dimensional (2D)
dimerized S = 1/2 Heisenberg model. We focus on the scaling correction in the
short-time region. A unified scaling form including both short-time and
finite-size corrections is proposed. According to this full scaling form,
improved short-imaginary-time scaling relations are obtained. We numerically
verify the scaling form and the improved short-time scaling relations for
different initial states using projector quantum Monte Carlo algorithm.
