This is possible with the $GUESS EXTRA keyword and $EXTRAF group. How this works is explained on page 78-79 of the manual. In short, you will need to use the $VEC group from the 6-31G(d) calculation in the input for the 6-31G(d,p) calculation, specify
$GUESS GUESS=MOREAD NORB=
>If I have orbitals with basis set 6-31G(d) for example, and I want to get the new orbitals with basis set 6-31G(d,p), is it possible to get the new ( 6-31G(d,p) ) with upgrading the old ( 6,31G(d) )? Probably it can saving time without calculating the new ( 6-31G(d,p) ) from the very beginning.
[ This message was edited on Mon Feb 17 '14 at 6:21pm by the author ]