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Re: negative bond order !

Alex Granovsky
gran@classic.chem.msu.su


Dear Masoud,

both Mulliken and Lowdin population analyses are not very reliable,
especially for basis sets with diffuse functions. The origin of
the problems is that, strictly speaking (i.e., quantum mechanically),
there are no things like atomic charges or bond orders i.e. there
are no linear operators corresponding to these chemical "properties".
Therefore, any charge or bond order analysis scheme is based on some
assumptions and is approximate by its nature. In particular, one can
get negative bond orders which are solely the artifacts of the
computational scheme and not related to chemical concepts of anti-
bonding.

You can give a try to Bader's analysis or NBO. With Firefly, you can
create input files for the former, while the latter is incorporated
directly.

Kind regards,
Alex Granovsky


On Thu Jan 3 '13 0:51am, Masoud Nahali wrote
--------------------------------------------
>>Hi

>In the following you can see the Mulliken population and bond order analysis that were calculated by FF for
>a [Al13]- cluster. The Mulliken charge on atom 6 and the large negative "bond orders" seems too unreasonable.
>Could the "bond order" get a negative value ? It may come from some non-orthogonality issues !!
>At first I want to ask that there is a way to improve the result without using NBO ? I have already calculated the NBO charges and bond-orders. Also I would like to know the definition that used in FF to calculate the bond order. We may try to improve it if there is not any major mistake in my input file. I appreciate any help
>to understand the issue and propose a way to figure it out. Sincerely Yours, m

>Best Wishes
>Masoud Nahali
>SUT
>
>
>input:
> $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE DFTTYP=B3LYP MAXIT=800
>  icharg=-1 MULT=1 d5=.t. icut=10 NZVAR=33 $END
> $SYSTEM TIMLIM=52560000 MWORDS=40 $END
> $BASIS GBASIS=N31 NGAUSS=6 NDFUNC=2 DIFFSP=.true. $END
> $SCF DIRSCF=.TRUE. NCONV=5 DAMP=.t. SHIFT=.t. MAXDII=50 $END
> $STATPT OPTTOL=0.0001 NSTEP=150 $END
> $DATA
>Title
>C1
> AL         13.0  -0.7218647681  -2.2191675894   1.2745396520
> AL         13.0  -2.3337805389   0.0000700618   1.2744204278
> AL         13.0  -0.7217890884   2.2192189335   1.2744228805
> AL         13.0   1.8880070112  -1.3719472552   1.2740325175
> AL         13.0   1.8880008432   1.3721011729   1.2740388462
> AL         13.0  -0.0000282245   0.0000509563  -0.0016174799
> AL         13.0  -0.7217096575  -2.2198204381  -1.2736785584
> AL         13.0  -2.3344647010  -0.0000285585  -1.2738398470
> AL         13.0  -0.7217513170   2.2197838036  -1.2739079247
> AL         13.0   1.8885522689  -1.3722067029  -1.2734889874
> AL         13.0   1.8885167082   1.3721188449  -1.2734966852
> AL         13.0   0.0009615294  -0.0001626788  -2.6306135437
> AL         13.0   0.0013499371  -0.0000105499   2.6291887024
> $END
>

>------------------------------------------------------------------------

>        TOTAL MULLIKEN AND LOWDIN ATOMIC POPULATIONS
>       ATOM         MULL.POP.    CHARGE          LOW.POP.     CHARGE
>    1 AL           13.612032   -0.612032        13.058957   -0.058957
>    2 AL           13.612219   -0.612219        13.057675   -0.057675
>    3 AL           13.612149   -0.612149        13.058959   -0.058959
>    4 AL           13.611334   -0.611334        13.060385   -0.060385
>    5 AL           13.611260   -0.611260        13.060392   -0.060392
>    6 AL            6.070675    6.929325        13.279058   -0.279058
>    7 AL           13.614674   -0.614674        13.058903   -0.058903
>    8 AL           13.614659   -0.614659        13.057611   -0.057611
>    9 AL           13.614684   -0.614684        13.058905   -0.058905
>   10 AL           13.613628   -0.613628        13.060381   -0.060381
>   11 AL           13.613781   -0.613781        13.060377   -0.060377
>   12 AL           13.904061   -0.904061        13.064086   -0.064086
>   13 AL           13.894843   -0.894843        13.064312   -0.064312

>          -------------------------------
>          BOND ORDER AND VALENCE ANALYSIS     BOND ORDER THRESHOLD=0.050
>          -------------------------------

>                   BOND                       BOND                       BOND
>  ATOM PAIR DIST  ORDER      ATOM PAIR DIST  ORDER      ATOM PAIR DIST  ORDER
>    1   2  2.828  0.690        1   3  4.577  0.238        1   4  2.829  0.689
>    1   5  4.578  0.237        1   6  2.739 -1.606        1   7  2.611  0.785
>    1   8  3.850  0.198        1   9  5.270  0.121        1  10  3.850  0.198
>    1  11  5.270  0.121        1  13  2.779  0.958        2   3  2.828  0.690
>    2   4  4.578  0.238        2   5  4.578  0.238        2   6  2.739 -1.608
>    2   7  3.850  0.198        2   8  2.611  0.784        2   9  3.850  0.198
>    2  10  5.270  0.121        2  11  5.270  0.121        2  13  2.780  0.958
>    3   4  4.578  0.237        3   5  2.829  0.689        3   6  2.739 -1.607
>    3   7  5.270  0.121        3   8  3.850  0.198        3   9  2.611  0.785
>    3  10  5.270  0.121        3  11  3.850  0.198        3  13  2.779  0.958
>    4   5  2.830  0.688        4   6  2.739 -1.603        4   7  3.850  0.198
>    4   8  5.270  0.121        4   9  5.270  0.121        4  10  2.611  0.785
>    4  11  3.850  0.198        4  13  2.778  0.957        5   6  2.739 -1.603
>    5   7  5.270  0.121        5   8  5.270  0.121        5   9  3.850  0.198
>    5  10  3.850  0.198        5  11  2.611  0.785        5  13  2.778  0.957
>    6   7  2.738 -1.623        6   8  2.738 -1.624        6   9  2.738 -1.623
>    6  10  2.738 -1.618        6  11  2.737 -1.619        6  12  2.695 -3.480
>    6  13  2.696 -3.430        7   8  2.829  0.692        7   9  4.578  0.239
>    7  10  2.830  0.691        7  11  4.578  0.239        7  12  2.780  0.964
>    8   9  2.829  0.692        8  10  4.579  0.239        8  11  4.579  0.239
>    8  12  2.781  0.964        9  10  4.579  0.239        9  11  2.830  0.692
>    9  12  2.780  0.964       10  11  2.830  0.691       10  12  2.779  0.964
>   11  12  2.779  0.964       12  13  5.391  0.571

>-----------------------------------------------------------------------------------


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