[molpro-user] No imaginary frequency but SURF cannot run

[Kenny W]

Dear Molpro Experts,
I tried to perform a VSCF/VCI calculation for a nine-atom anion in the doublet state, after the geometry optimization followed analytic frequency at MCSCF level. The frequencies reported were all positive values, however, the subsequent 1D SURF calculation complained about imaginary frequency and could not continue.
First, the MCSCF OPTG and FREQUENCY calculation keywords are shown as follows:
NOSYM;orient,massmass,isobasis={default=aug-cc-pwCVDZ}
{multi,energy=1.0e-8,gradient=1.0e-5,step=1.0e-5maxiter,40occ,50;closed,37;        !CAS(13,13)wf,87,1,1;natorb,print=20,ci,state=1.1}
{optg,maxit=100,gradient=1.0e-5,energy=1.0e-8,step=1.0e-5}pop;
{multi,energy=1.0e-8,gradient=1.0e-5,step=1.0e-5;cpmcscf,hess,accu=1.d-5maxiter,40occ,50;closed,37;  wf,87,1,1;natorb,print=10,ci,state=1.1}
{frequencies,analyticalprint,hessian,low}
put,molden,cas1313_awcdz_nosym_optfrq.molden;---
and the reported frequencies (all positive) are:
 _FREQUENCIES(1:27)   =      0.00001845     0.00001629     0.00000707     0.00000225     0.00001146     0.00001581                             7.52426274    58.84544984    64.37850876    70.83457530   103.14123353   126.11691779                           137.75677617   181.48189951   234.48735837   270.42956902   345.45378008   427.77056976                           461.65694834   524.95228098   531.51838006   575.23162819   586.87961440  1633.71618449                          1637.44993389  1999.82375492  2062.79045692
The second step was to calculate VSCF and VCI by restarting from the files 1 and 2 of the previous calculation:
 restart; file,1,vscf.int file,2,vscf.wfu file,3,vscf.res,newNOSYM;orient,massmass,isobasis={default=aug-cc-pwCVDZ}
label1{multi,energy=1.0e-8,gradient=1.0e-7,step=1.0e-5maxiter,40occ,50;closed,37;wf,87,1,1;state,1natorb,2141.3,state=1.1cpmcscf,grad,1.1,accu=1.d-9}
{surf,start1D=label1,ndim=3,dellog=1,sym=auto    !(3) generate PESscalnm,auto=onintensity,dipole=2}
vscf vci,pmp=3,version=1 vci,pmp=3,version=2---
The job bump out at SURF program, with the final dying message:
 You have an imaginary vibration. Please check the FREQ calculation.
However in the previous job all of the harmonic frequencies were found positive. May I know what was wrong with my SURF input? Thank you very much for your kind attentions.
==========MJ Wu 		 	   		  
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