Subject: semiempirical methods...

From: Mike Peleah <[email-masked]>
Date: Thu, 27 Sep 2001 21:27:18 +0300

Dear CHEMISTRY,

I tried to make calculation to compare results of nonempirical methods
for heterocyclic compounds. I used isatin (attached gif with structure
and  original  xyz coordinates), based on X-Ray data from Н.А.Фролова,
В.Х.Кравцов,  В.Н.Биюшкин,  Ю.М.Чумаков, О.Н.Белькова, Т.И.Малиновский
"Кристаллическая   и   молекулярная   структура   изатина"  //  Журнал
Структурной Химии, ╧3, т.29, 1988, с.155-158.

Here are some results (I used ArgusLab v.2.0):
                   EHT     AM1    PM3      MNDO   INDO/1S
Energy, au     -34.63   -71.19   -65.11   -71.36   -81.29
ZDO Charges                                             
C 1           +0.7977  +0.2242  +0.2733  +0.2420  +0.3029
C 2           +0.9255  +0.2654  +0.1588  +0.3100  +0.4211
N 3           -0.0723  -0.3099  +0.1444  -0.3231  -0.1980
C 4           +0.3339  +0.0750  -0.0778  +0.1121  +0.1014
C 5           -0.0155  -0.1669  -0.1362  -0.0962  -0.0442
C 6           +0.0842  -0.0904  -0.0634  -0.0178  -0.0198
C 7           -0.0019  -0.1631  -0.1335  -0.0933  -0.0440
C 8           +0.1194  -0.0372  -0.0096  +0.0362  +0.0286
C 9           -0.0002  -0.1752  -0.1791  -0.1804  +0.0085
O 10          -0.9301  -0.1791  -0.2093  -0.1992  -0.4093
O 11          -1.0887  -0.2824  -0.3251  -0.3008  -0.4859
H 12          +0.1199  +0.2732  +0.1072  +0.2337  +0.1861
H 13          -0.0669  +0.1361  +0.1107  +0.0662  +0.0321
H 14          -0.0645  +0.1368  +0.1047  +0.0635  +0.0361
H 15          -0.0685  +0.1360  +0.1075  +0.0646  +0.0328
H 16          -0.0720  +0.1574  +0.1274  +0.0826  +0.0515

The  thing  I surprised most is a _sharp_ difference in energies -- in
average more than 10 au. Another thing that I find very interesting is
differ of charges on C1/C2/N3/H12 atoms in PM3 from all other methods.

Could anybody help me?

Best regards,
 Mike                          mailto:[email-masked]

---

From: elewars <[email-masked]>
Date: Fri, 28 Sep 2001 12:12:55 -0400

Hello,

I think your energies are heats of formation (probably in kcal/mol), not a.u.
or hartrees (you get hartrees in ab initio calculations). The EH method was
never taken seriously for quantitative work; its value lies in its wide range
of applicability and its speed, combined with good intuition (= Roald
Hoffmann). The other three method's energies are not really in much
disagreement, by curent SE standards (see reviews by Dewar and by Stewart).
Yes, the PM3 charge for N3 is odd.

E. Lewars
======

Mike Peleah wrote:

> and  original  xyz coordinates), based on X-Ray data from î.á.æÒÏÌÏ×Á,
> ÷.è.ëÒÁ×ÃÏ×,  ÷.î.âÉÀÛËÉÎ,  à.í.þÕÍÁËÏ×, ï.î.âÅÌØËÏ×Á, ô.é.íÁÌÉÎÏ×ÓËÉÊ
> "ëÒÉÓÔÁÌÌÉÞÅÓËÁÑ   É   ÍÏÌÅËÕÌÑÒÎÁÑ   ÓÔÒÕËÔÕÒÁ   ÉÚÁÔÉÎÁ"  //  öÕÒÎÁÌ
> óÔÒÕËÔÕÒÎÏÊ èÉÍÉÉ, ¹3, Ô.29, 1988, Ó.155-158.
>
>   ------------------------------------------------------------------------
>                  Name: isatin.gif
>    isatin.gif    Type: GIF Image (image/gif)
>              Encoding: base64
>
>              Name: iz.xyz
>    iz.xyz    Type: application/x-unknown-content-type-XYZ_auto_file
>          Encoding: base64