Ceilidh ... Re: negative bond order !

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Re: negative bond order !

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

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

Thu Jan 3 '13 8:22pm

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