[molpro-user] df-lmp2 to describe the pi-stacking of bezene

[Grant Hill]

Hello all,

I'm attempting to use df-lmp2 to describe the pi-pi stacking interaction
of two benzenes with molpro 2002.10. Following the guidance in the
molpro manual I have separated the two monomers (with both vertical and
horizontal separations of 55 angstroms) to obtain orbital domains which
are then re-used at the geometry I'm interested in. However, I'm having
a few problems:

1). At both the well-separated and interacting distances the Pipek-Mezey
orbital localisation fails to converge.

2). With both the failed Pipek-Mezey localisation and Boys localisation
the energy of the well-separated system when compared with that of twice
the benzene monomer energy suggests that there is still some interaction
despite the large separation (order of 0.002 hartree).

3). The binding energy obtained for the distance I'm interested in with
Boys localisation is of the order of a repulsive hartree!!!

I'm unsure of how to proceed with this calculation, does anyone have any
advice either on what I may be doing wrong or how I can get the
Pipek-Mezey localisation to converge? A sample input file follows for
reference.

Thanks in advance,

Grant Hill



***,benzene para-disp dimer df-lmp2/cc-pVDZ SP on vert sep of 3.5
memory,70,m
gdirect,page=1

text,SP calculation on benzene monomer

basis={
default,cc-pVDZ
set,df
spd,c,vdz-mp2-aux
sp,h,vdz-mp2-aux
}

geometry={
nosym,noorient,ang
Q
c   1 1.39913961
c   1 1.39913961       2 60.0
c   1 1.39913961       3 60.0         2 180.0
c   1 1.39913961       4 60.0         3 180.0
c   1 1.39913961       5 60.0         4 180.0
c   1 1.39913961       6 60.0         5 180.0
h   2 1.08389954       3 120.0        4 180.0
h   3 1.08389954       4 120.0        5 180.0
h   4 1.08389954       5 120.0        6 180.0
h   5 1.08389954       6 120.0        7 180.0
h   6 1.08389954       7 120.0        2 180.0
h   7 1.08389954       2 120.0        3 180.0
end

}

hf
e_hf_benz=energy
locali,boys

df-lmp2,basis=df
e_benzene=energy

text,Benzene dimer large separation

geometry={
nosym,noorient,ang
Q
c   1 1.39913961
c   1 1.39913961       2 60.0
c   1 1.39913961       3 60.0         2 180.0
c   1 1.39913961       4 60.0         3 180.0
c   1 1.39913961       5 60.0         4 180.0
c   1 1.39913961       6 60.0         5 180.0
h   2 1.08389954       3 120.0        4 180.0
h   3 1.08389954       4 120.0        5 180.0
h   4 1.08389954       5 120.0        6 180.0
h   5 1.08389954       6 120.0        7 180.0
h   6 1.08389954       7 120.0        2 180.0
h   7 1.08389954       2 120.0        3 180.0
Q   1 55.0      2 90.0         3 180.0
Q  14 55.0      1 90.0         2 -90.0
c  15 1.39913961    14 90.0        1 90.0
c  15 1.39913961    16 60.0        14 90.0
c  15 1.39913961    17 60.0        16 180.0
c  15 1.39913961    18 60.0        17 180.0
c  15 1.39913961    19 60.0        18 180.0
c  15 1.39913961    20 60.0        19 180.0
h  16 1.08389954       17 120.0       18 180.0
h  17 1.08389954       18 120.0       19 180.0
h  18 1.08389954       19 120.0       20 180.0
h  19 1.08389954       20 120.0       21 180.0
h  20 1.08389954       21 120.0       16 180.0
h  21 1.08389954       16 120.0       17 180.0
end

}

hf
e_hf_sep=energy
locali,boys

df-lmp2,basis=df,save=4000.2
e_sep=energy

text,Benzene stack vert separated by 3.5 ang

geometry={
nosym,noorient,ang
Q
c   1 1.39913961
c   1 1.39913961       2 60.0
c   1 1.39913961       3 60.0         2 180.0
c   1 1.39913961       4 60.0         3 180.0
c   1 1.39913961       5 60.0         4 180.0
c   1 1.39913961       6 60.0         5 180.0
h   2 1.08389954       3 120.0        4 180.0
h   3 1.08389954       4 120.0        5 180.0
h   4 1.08389954       5 120.0        6 180.0
h   5 1.08389954       6 120.0        7 180.0
h   6 1.08389954       7 120.0        2 180.0
h   7 1.08389954       2 120.0        3 180.0
Q   1 1.6      2 90.0         3 180.0
Q  14 3.5      1 90.0         2 -90.0
c  15 1.39913961    14 90.0        1 90.0
c  15 1.39913961    16 60.0        14 90.0
c  15 1.39913961    17 60.0        16 180.0
c  15 1.39913961    18 60.0        17 180.0
c  15 1.39913961    19 60.0        18 180.0
c  15 1.39913961    20 60.0        19 180.0
h  16 1.08389954       17 120.0       18 180.0
h  17 1.08389954       18 120.0       19 180.0
h  18 1.08389954       19 120.0       20 180.0
h  19 1.08389954       20 120.0       21 180.0
h  20 1.08389954       21 120.0       16 180.0
h  21 1.08389954       16 120.0       17 180.0
end

}

hf
locali,boys

df-lmp2,basis=df,start=4000.2
put,molden,df-lmp2-sep.molden
e_dflmp2=energy

e_hf_diff=(e_hf_sep-(2*e_hf_benz))
e_diff=(e_sep-(2*e_benzene))            !Diff between benzene    
                                        !monomer and large sep
e_bind_dflmp2=(e_dflmp2-(2*e_benzene))  !Interaction energy
e_dind_dfkcal=e_bind_dflmp2*tokcal      !convert to kcal/mol