  The merging of double white dwarfs (WDs) may produce the events of
accretion-induced collapse (AIC) and form single neutron stars (NSs).
Meanwhile, it is also notable that the recently proposed WD+He subgiant
scenario has a significant contribution to the production of massive double
WDs, in which the primary WD grows in mass by accreting He-rich material from a
He subgiant companion. In this work, we aim to study the binary population
synthesis (BPS) properties of AIC events from the double WD mergers by
considering the classical scenarios and also the contribution of theWD+He
subgiant scenario to the formation of double WDs. First, we provided a dense
and large model grid of WD+He star systems for producing AIC events through the
double WD merger scenario. Secondly, we performed several sets of BPS
calculations to obtain the rates and single NS number in our Galaxy. We found
that the rates of AIC events from the double WD mergers in the Galaxy are in
the range of 1.4-8.9*10^-3 yr^-1 for all ONe/CO WD+ONe/CO WD mergers, and in
the range of 0.3-3.8*10^-3 yr^-1 when double COWD mergers are not considered.We
also found that the number of single NSs from AIC events in our Galaxy may
range from 0.328*10^7 to 1.072*10^8. The chirp mass of double WDs for producing
AIC events distribute in the range of 0.55-1.25 Msun. We estimated that more
than half of doubleWDs for producing AIC events are capable to be observed by
the future space-based gravitational wave detectors.
