.DF\*deg =<<000011110000//
001111111100//
011100001110//
011000000110//
110000000011//
110000000011//
110000000011//
110000000011//
011000000110//
011100001110//
001111111100//
000011110000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000//
000000000000>>
.DF\np =\thsp \nthsp
.NF<>
.PN33
.LM10
.RM80
.FJ
.CM------------------------------------------------------------------
.HF<>
.RL55
#BD.8 GAUSSIAN 90 VERSION#N

#ID.8.0 Introduction to GAUSSIAN 90 version#N

\np The GAUSSIAN 90 version of the NBO program differs from its
predecessors in that the NBO segments are included as an organic
link (Link 607) of the GAUSSIAN 90 standard route, rather than
as a ``fix'' on Link 601.  Default NBO analysis is invoked by simply
including the ``ExtraLinks=L607'' option on the main route card
(or by adding Link 607 to any non-standard route).  Various non-default
NBO options are invoked by setting IOp(40)=1 in Overlay 6 (see Section D.8.1)
and including $NBO keylists in the usual way.


#ID.8.1 GAUSSIAN 90 sample input#N

\np A sample GAUSSIAN 90 input file to
recreate the default methylamine (RHF/3-21G at Pople-Gordon idealized geometry)
output displayed in Section A.3 is shown below:

.DF\@seg =
# RHF/3-21G ExtraLinks=L607

Methylamine...RHF/3-21G//Pople-Gordon standard geometry

 0   1
 C
 N   1   CN
 H   1   CH   2   tet
 H   1   CH   2   tet   3   120.  0
 H   1   CH   2   tet   3   240.  0
 H   2   NH   1   tet   3    60.  0
 H   2   NH   1   tet   3   300.  0

 CN        1.47
 CH        1.09
 NH        1.01
 tet     109.4712

.ED
.LJ
.RL23
.HR<<3//+1//5//85>>
.LM5
.RM85
 #T

.RS#^
\@seg
.RS^#

.HR<<3//+0//5//85>>
.FJ
.LM10
.RM80

\np #N(The $NBO keylist is not needed to perform the default
NBO analysis with GAUSSIAN 90.)

.NP
\np The following sample input file demonstrates how to select non-default
options or analyses, such as the NLMO analysis
(Section B.6.2) and the dipole analysis (Section B.6.3):

.DF\@seg =
# RHF/3-21G ExtraLinks=L607 IOp(6/40=1)

Methylamine...RHF/3-21G//Pople-Gordon standard geometry

 0   1
 C
 N   1   CN
 H   1   CH   2   tet
 H   1   CH   2   tet   3   120.  0
 H   1   CH   2   tet   3   240.  0
 H   2   NH   1   tet   3    60.  0
 H   2   NH   1   tet   3   300.  0

 CN        1.47
 CH        1.09
 NH        1.01
 tet     109.4712

$NBO  NLMO  DIPOLE  $END

.ED
.LJ
.RL23
.HR<<3//+1//5//85>>
.LM5
.RM85
 #T

.RS#^
\@seg
.RS^#

.HR<<3//+0//5//85>>
.FJ
.LM10
.RM80

\np #NNote that IOp(40) must be set to 1 whenever an $NBO keylist is
included in the GAUSSIAN 90 input file.

\np #NThe keylists of the NBO program should always appear at the bottom of the
GAUSSIAN 90 input file and should be ordered: $NBO, $CORE, $CHOOSE, $DEL.
NBO job options are selected by inserting their
associated keywords (Section B.2) into the $NBO keylist.  All NBO keywords
are applicable to the electronic wavefunctions computed by the GAUSSIAN 90
programs.  It is advisable to terminate the GAUSSIAN 90 input file with
a blank line.

\np If the NBO program 
encounters the end-of-file while searching for a keylist, the input file
is rewound and the search for the keylist is continued.  This is particularly
useful for jobs which call the NBO analysis several times.  For example, an
MP2 calculation with the GAUSSIAN 90 option DENSITY=ALL causes Link 607 to
loop over three densities (SCF, Rho2, and MP2), and hence, the NBO analysis
is called three times, once for each density.  A single $NBO keylist
(and $CORE and $CHOOSE keylists) will suffice as input for all three analyses.
Alternatively, separate $NBO keylists, one for each density, could be inserted
at the bottom of the GAUSSIAN 90 input file.

.NP
\np The IOp parameters 40-43 of Link 607 exert additional control over the
NBO program, as listed below:

.LM+5
.RL30
.TB
.FM<<1L10//0C10//0L40>>
.RW-
.RW<>
.RW=
.RW<>
.RW<< //-1//perform the NPA only>>
.RW<< //0//perform the default NBO analysis>>
.RW<< //1//perform the NBO analysis>>
.RW<< // //(read keywords in $NBO keylist)>>
.RW<< //2//initiate NBO energetic analysis>>
.RW<< //3//complete NBO energetic analysis>>
.RW
.RW<>
.RW<< //1//MP first order density>>
.RW<< //2//MP2 density>>
.RW<< //3//MP3 density>>
.RW<< //4//MP4 density>>
.RW<< //5//CI one-particle density>>
.RW<< //6//CI density>>
.RW<< //7//QCI/CC density>>
.RW<< //8//density correct to second order>>
.RW
.RW<>
.RW<< // //(force the DIPOLE keyword)>>
.RW
.RW<>
.RW<< // //(force the RESONANCE keyword)>>
.RW-
.ET
.LM-5

#NBy default, the NBO analysis will be performed on the density matrix
for the current wavefunction.  In general, it is preferable to activate
the DIPOLE and RESONANCE options by keywords in the $NBO keylist rather
than via the IOp parameters.

.NP
#ID.8.2 NBO energetic analysis#N

\np Due to the overlay structure of the GAUSSIAN 90 programs, a non-standard
route must be employed to perform the NBO energetic analysis.  The following
table lists and describes the tasks of the GAUSSIAN 90 links in the order that
they appear in the non-standard route:

.RL24
.LM+24
.RM-2
.OS<<24//#ILINK#N>>
#IDESCRIPTION#N
.HR<<1//+1//10//32>>
.HR<<1//+1//34//80>>

.OS<<24//6/40=1/7;>>
Perform the normal NBO analysis, storing information about the NBOs for
the NBO energetic analysis on the FILE48 direct access file.

.OS<<24//6/40=2/7(1);>>
Read the next deletion listed in the $DEL keylist.  If there are no more
deletions, move to the next link.  Otherwise, compute the modified density
matrix, store it on the read-write files, and skip the next link in the
non-standard route.

.OS<<24//99/5=1,9=1/99;>>
Finish GAUSSIAN 90 execution.

.OS<<24//5/7=1,13=1/1,2;>>
Using the modified density matrix, compute the deletion energy by
a single pass through the SCF energy evaluator.  Store the deletion energy
on the read-write files.

.OS<<24//6/40=3/7(-3);>>
Read the deletion energy from the read-write files and complete the energetic
analysis.  Step backwards, in the non-standard route, three links.

.HR<<1//+0//10//80>>
.LM-24
.RM+2

\np The following is a GAUSSIAN 90 input file
that will generate, in addition to the default NBO output, the NBO energetic
(Section B.6.10) analysis of methylamine:

.DF\@seg =
# NONSTD
1//1;
2//2;
3/5=5,11=1,25=14,30=1/1,2,3,11,14;
4/7=1/1;
5//1;
6/7=2,8=2,9=2,10=2,19=1,40=1/1,7;
6/40=2/7(1);
99/5=1,9=1/99;
5/7=1,13=1/1;
6/40=3/7(-3);

Methylamine...RHF/3-21G//Pople-Gordon standard geometry

 0   1
 C
 N   1   CN
 H   1   CH   2   tet
 H   1   CH   2   tet   3   120.  0
 H   1   CH   2   tet   3   240.  0
 H   2   NH   1   tet   3    60.  0
 H   2   NH   1   tet   3   300.  0

 CN        1.47
 CH        1.09
 NH        1.01
 tet     109.4712

$NBO  $END
$DEL  NOSTAR
      ZERO 2 ATOM BLOCKS   4  BY  3
                           1  3  4  5
                           2  6  7
                           3  BY  4
                           2  6  7
                           1  3  4  5
$END
.ED
.LJ
.HR<<3//+1//5//85>>
.LM5
.RM85
 #T

.RS#^
\@seg
.RS^#

.HR<<3//+0//5//85>>
.FJ
.LM10
.RM80

\np #NNote that for the GAUSSIAN 90 version of the NBO program, each deletion
in the $DEL keylist must begin on a new line of the input file (the first
deletion can follow the ``$DEL'' keylist identifier, as shown above).  The
``$END'' keylist terminator must also appear on its own line.

.NP
#ID.8.3 Geometry reoptimization with NBO deletions#N

\np The structural effects of electron delocalization can be examined
by coupling the NBO energetic analysis to the Fletcher-Powell (numerical)
geometry optimization routines of the GAUSSIAN 90 package.  The
following GAUSSIAN 90 input file will reoptimize selected internal
coordinates of RHF/3-21G methylamine in the absence of its strong
#In#N#dN#u\rarr \sigma #u*#d#d#>
.LM5
.RM85
 #T

.RS#^
\@seg
.RS^#

.HR<<3//+0//5//85>>
.FJ
.LM10
.RM80

\np #NReoptimization of the internal coordinates specified in this example
leads to lengthening of the C-N bond (1.513\thsp \ang ) and closing of
the H-C-N bond angle (108.3\thsp \*deg ), as expected from
lone pair/antibond overlap arguments.  The C-H bond length contracts
(1.075\thsp \ang ) due to the removal of electron density from its antibond.

\np #NNote that the numerical optimization routines of the GAUSSIAN 90 program
must be employed since analytic gradients are not available for the modified
wavefunction of the NBO energetic analysis.  Hence, these optimizations are
time-consuming, generally requiring 8#In#N-12#In#N single point
calculations (#In#N = number of symmetry unique internal coordinates) before
convergence of the gradients is obtained (the example requires 28 single
point calculations before convergence).  Careful selection of the coordinates
to be optimized is recommended.


.RL20
#ID.8.4 NBO program installation#N

\np The NBO program link is installed automatically by the installation
procedure for the GAUSSIAN 90 programs.


.RL50
#ID.8.5 NBO communication with GAUSSIAN 90#N

\np The NBO driver routines (RUNNBO, FEAOIN, DELSCF) access the following
GAUSSIAN 90 routines, read-write files, and COMMON blocks:

#_GAUSSIAN 90 routines:#/#T

    SR CharPn(IString)
    SR DENGET(IOut,IODens,IMeth,LenDen,GotIt,P)
    FN ILSW(IOPER,WHERE,WHAT)
    FN InToWP(Nints)
    FN ITqry(Ifile)
    SR TRead(IARN,X,M,N,MM,NN,K)
    SR TWrite(IARN,X,M,N,MM,NN,K)

#N#_GAUSSIAN 90 read-write files:#/

.LM+5
.TB
.FM<<1C8//2L45>>
.RW-
.RW<>
.RW=
.RW<<501//Total energy>>
.RW<<502//Job title>>
.RW<<506//Basis set information>>
.RW<<512//Effective core potential information>>
.RW<<514//AO overlap matrix>>
.RW<<518//AO dipole integrals>>
.RW<<524//MO coefficients (alpha)>>
.RW<<526//MO coefficients (beta)>>
.RW<<528//SCF density matrix (alpha)>>
.RW<<530//SCF density matrix (beta)>>
.RW<<536//AO Fock matrix (alpha)>>
.RW<<538//AO Fock matrix (beta)>>
.RW<<603//AO density matrix>>
.RW<<636//NBODAF filename>>
.RW-
.ET
.LM-5

#_GAUSSIAN 90 COMMON blocks:#/#T

    COMMON/MOL/NATOM,ICHARG,MULTIP,NAE,NBE,NE,NBASIS,IAN(401),
   +           ATMCHG(400),C(1200)
    COMMON/LP2/NLP(1600),CLP(1600),ZLP(1600),KFIRST(400,5),
   +  KLAST(400,5),LMAX(400),LPSKIP(400),NFroz(400)
    COMMON/B/EXX(6000),C1(6000),C2(6000),C3(6000),X(2000),Y(2000),
   +     Z(2000),JAN(2000),SHELLA(2000),SHELLN(2000),SHELLT(2000),
   +     SHELLC(2000),AOS(2000),AON(2000),NSHELL,MAXTYP
    INTEGER SHELLA,SHELLN,SHELLT,SHELLC,SHLADF,AOS,AON
    DIMENSION C4(2000),SHLADF(2000)
    EQUIVALENCE(C4(1),C3(2001)),(SHLADF(1),C3(4001))
 #N