Trouble Pasting

There is data is columns A:C. I can't paste my selected calc with the following.... Your help would be greatly appreciated. Thanks

Sub aaaa()
Dim lw As Long
    Range("D1").Select
    ActiveCell.FormulaR1C1 = "=R[1]C[-2]-RC[-2]"
    Range("D1:D2").Select 'D2 is blank. I need the calc in D1 to be copied to every other cell in the range
    Selection.Copy
    lw = Range("A" & Rows.Count).End(xlUp).Row 'Select cells in column D only if there is data in A
    Range("D1:D" & lw).Select
    ActiveSheet.Paste 'I lose the ability to paste D1:D2 to the selected range.
'   I can copy the selection to D:D, but I get 65,000 rows I don't want.
    Application.CutCopyMode = False
End Sub