看了xtabond2命令，里面提到这样一句话：
xtabond2 shares features of all estimation commands; see help estcom.

然后点击estcom，出现其帮助文件，里面提到

11. Estimation statistics
    Command estat displays scalar- and matrix-valued postestimation statistics such as AIC and BIC.

12. Variance-covariance matrix of the estimators (VCE)
    Command estat vce displays the VCE -- either as a covariance matrix or as a correlation matrix.
    You can obtain the coefficients and VCE into Stata matrices by using e(b) and e(V) in expressions.
    You can obtain the coefficients and VCE into Mata matrices by using st_matrix(e(b)) and st_matrix(e(V)); see [M-5] st_matrix().

为何我在xtabond2命令运行之后，用estat ic，提示错误，而没有得出AIC值

如果这个方法不可行，应该如何才能得到AIC值？