# BSSE calculations

Wheeler, Dr M.D. mdw10 at leicester.ac.uk
Fri Sep 21 17:38:24 BST 2001

```Dear All,
I am currently trying to map out the PES of various Rg-CC complexes,
however, I am running in to a few problems.  When I do the calculations
using a do loop in the input file there appears to be a problem close to
linear geometries.  Depending upon which direction I scan the PES I get
very different answers (a minimum if I increase theta and a maximum if I
decrease theta), I use the following input file,

***, CC-Rg intermolecular PES, CCSD(T), aug-cc-pVDZ basis
Memory,80,m;
basis=avtz                                     !basis set
!****define internal
coordinates for complex****
rcc=1.25                                       !CC bond-length
rc=rcc*0.5                                     !distance of C from
center of mass, RC
distances=[3.825]
!distances of Rg from
center of mass, R_Rg
angles=[170,175,180]
!Rg-CoM-C angle, theta
geometry={x,angstrom;                          !****define RgCC complex
using two dummy atoms****
q1;
q2,q1,5.0;
c1,q1,rc,q2,90.0;
c2,q1,rc,q2,270.0,c1,0.0;                      !geometry of CC
ne,q1,r_rg(i),q2,90.0,c1,theta(i)              !geometry of Rg
}
!****start loop over
variables****
i=0
do ith=1,#angles
do ir=1,#distances
i=i+1
r_rg(i)=distances(ir)
theta(i)=angles(ith)
!****start actual
calculation here****
text,calculation for complex
dummy
hf;                                            !SCF for total system
e_complex_hf(i)=energy                         !save energy in variable
e_complex_hf(i)
ccsd(t);                                       !CCSD(T) for total
system
e_complex(i)=energy                            !save energy in variable
e_complex(i)

text,cp calculation for CC
dummy,ne                                       !make Rg a dummy center
hf;                                            !scf for CC
e_cc_hf(i)=energy                              !save energy in variable
e_cc_hf(i)
ccsd(t);                                       !CCSD(T) for CC
e_cc(i)=energy                                 !save energy in variable
e_cc(i)

text,cp calculation for Rg
dummy,c1,c2                                    !make CC dummy
hf;                                            !scf for Rg
e_rg_hf(i)=energy                              !save energy in variable
e_rg_hf(i)
ccsd(t);                                       !CCSD(T) for Ne
e_rg(i)=energy                                 !save energy in variable
e_rg(i)

de_cp_hf(i)=(e_complex_hf(i)-e_cc_hf(i)-e_rg_hf(i))*tocm
de_cp(i)=(e_complex(i)-e_cc(i)-e_rg(i))*tocm
enddo
enddo

!****exit loop and
create table of results****
!table,theta,r_rg,e_complex_hf,e_cc_hf,e_rg_hf,de_cp_hf,e_complex,e_cc,e
_rg,de_cp
table,theta,r_rg,de_cp
theta(Deg),R_Rg(ang),E_complex_hf,E_CC_hf,E_Rg_hf,De(CP_cor)_hf,\
! E_complex,E_CC,E_Rg,De(CP_cor)
save,necc_bend_test_x.tab
! title,Results for Ne-CC (energies in cm-1), basis \$basis
---;

Can anyone suggest why this might be happening...???

Martyn

----------------------------------------------
Dr. Martyn D. Wheeler
Department of Chemistry
University of Leicester