# Difficulties with CCSD(T)

Wheeler, Dr M.D. mdw10 at leicester.ac.uk
Thu Mar 14 13:26:46 GMT 2002

```Dear All,

I seem to be getting some spurious results while trying to run CCSD(T)
calculations on the BaNC/BaCN pes.  The RHF-SCF values give a nice
smooth PES but the CCSD(T) results seem to exhibit some slight
discontinuities.  Worse still is when I try and repeat soem of the areas
of the PES I get different results in the single point calculations as
compared with the PES scan.  I have enclosed my input file.  If I am
doing something daft could someone give me a point in the right

Martyn

***,BaCN, RCCSD(T) PES scan
Memory,64,m;
cartesian;
!set up geometry for BaCN
ncom = 0.4616472                !CN centre of mass wrt n atom
ccom = 1.0 - ncom
n_r_ba   = [2.80]
!n_r_ba   = [3.20,3.00,2.80,2.70,2.30,2.10,1.80]
!n_r_ba   = [3.40,3.60,4.00,4.40,4.80,5.50,6.50,7.00]
n_r      = 1.17497
!n_theta
=[15.0,30.0,45.0,60.0,75.0,90.0,105.0,120.0,135.0,150.0,165.0,180.0]
n_theta  = [30.0]
r_n  = ncom * n_r
r_c  = ccom * n_r

geometry={z; angstrom;
q1;
q2,q1,5.0;
n,q1,r_n,q2,90.0;
c,q1,r_c,q2,270.0,n,0.0;
ba,q1,r_ba(i),q2,90.0,n,theta(i)
}

i=0                                 !initialise counter
do i1=1,#n_theta
do i2=1,#n_r_ba
i = i + 1                  !step counter
theta(i) = n_theta(i1)     !set distances and angles in
Z-matrix
r_ba(i) = n_r_ba(i2)

!set up basis set for Ba using ECP2 and vdz for C and N
basis={
ecp,ba,ecp2;                                   !ECP INPUT
!Basis functions for Ba
ba = mbs-ecp2;
!Basis functions for N and C
c = cc-pVDZ;
n = cc-pVDZ;
}

!Generate a crude set of RHF orbitals for the BaCN geometry
rhf;occ,10,2;closed,9,2;wf,23,1,1;
e_rhf_small(i) = energy;

!set up basis set for Ba using ECP of Bauschlicher et al and
vtz for C and N
basis={
ecp,ba,46,3;                                   !ECP INPUT
7;                                             !LOCAL POTENTIAL
0,853.12734,-0.15015859;1,365.63595,-31.091521;
2,135.40773,-324.30893;2,41.372199,-156.27903;
2,13.793461,-56.907784;2,4.5377522,-24.555412;
2,1.4987754,-3.4615665;
9;                                             !S POTENTIAL
0,238.39452,2.9039160;1,152.54120,41.889969;
2,87.201623,459.03195;2,27.984671,247.05494;
2,4.2732489,955.86400;2,3.5116944,-1749.4400;
2,2.6668111,1403.8815;2,2.0994424,-734.60817;
2,1.8396739,228.66824;
12;                                            !P POTENTIAL
0,214.14717,4.9304099;1,200.53808,35.877654;
2,102.74840,801.48414;2,29.528894,343.51853;
2,3.7755668,11.532450;2,3.7419617,1160.7035;
2,2.9773058,-2478.1943;2,2.3776970,1867.3921;
2,1.7806361,-543.91415;2,1.3342370,98.812770;
2,1.0286679,-11.238580;2,0.85111593,1.1348389;
11;                                            !D POTENTIAL
0,204.21581,6.9692195;1,167.42937,38.886122;
2,109.16583,864.82033;2,40.436261,444.80000;
2,13.423074,169.50031;2,3.9384434,62.535558;
2,1.1846942,10.804797;2,0.74187473,-35.985792;
2,0.66746916,74.358847;2,0.57560952,-60.369719;
2,0.51979646,21.780014;
!Basis functions for Ba
s,ba,4.7718403,2.9123522,1.6302193;
c,1.3,-0.050091,0.203485,-0.352163;
s,ba,0.55521818,0.23165492,0.075,0.025,0.008;
p,ba,4.7577636,2.9926680,1.7446629;
c,1.3,-0.026545,0.069270,-0.096490;
p,ba,0.53509088,0.20679664,0.069,0.023,0.0076666,0.0025556;
d,ba,1.17,0.39,0.13;
c,1.3,0.010769,-0.369779,-0.577784;
d,ba,0.7,0.043,0.01433;
f,ba,0.3135459,0.1072716;
c,1.2,0.745210,1.029279;
f,ba,0.1392423,0.0476382;
c,1.2,0.330940,0.457091;
!Basis functions for N and C
c = d-aug-cc-pVTZ;
n = d-aug-cc-pVTZ;
}

!Use orbitals from small basis set as start to large RHF calc.
rhf;occ,10,2;closed,9,2;wf,23,1,1;start,2100.2;
e_rhf_big(i) = energy;

!Now do an RCCSD(T) calcualtion with the large basis set
rccsd(t);
e_ccsdt(i) = energy;

!Write table out to a file during the calcuation

table,r_ba(i),theta(i),e_rhf_small(i),e_rhf_big(i),e_ccsdt(i);save,bacn_
short_2.tab;
enddo
enddo

table,r_ba,theta,e_rhf_small,e_rhf_big,e_ccsdt;save,test_new.tab;
---;

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