can you default the G/L account in Purchase order?

If a material has no material code in SAP, can you default the G/L account in Purchase order or it has to be manually entered?.
If a material has no material code in SAP, we can still, default the G/L account with the help of material groups. We can assign the valuation class to a material group and then in FI-automatic posting, we can assign the relevant G/L account in the Transaction event key. The assignment of a valuation class to a material group enables the system to determine different G/L accounts for the individual material groups.