# [molpro-user] Convergence Problem in MCSCF Calculations

Peter Knowles KnowlesPJ at Cardiff.ac.uk
Mon Jan 26 10:34:36 GMT 2009

```It looks to me as if your calculations nearly converge, and would do
so with just a few more iterations in the MCSCF equation solver, which
can be specified using the MAXITER command - see http://www.molpro.net/info/current/doc/manual/node252.html
Of course, 0.4 Angstrom is a very short bond length giving very high
ground-state energies, and one can expect all kinds of challenges from
low-lying states that might affect the choice of active orbital space.
Peter
On 26 Jan 2009, at 05:46, Sunil wrote:

> Dear Sir,
>
> I am facing a convergence problem when using Molpro to calculate
> potential energy surfaces of CO2 molecule. The input of the program
> is as follows:
>
>
> *** CO2 PE curve                        ! Title: PE Curve for CO2
> memory,32,m
> maxiter=100
> geomtyp=zmat
> geometry
> ang                                     ! ang is used if we intend
> to provide distance in Angstrom; default for Z-matrix is au
> C
> O1 C rco1(i)
> O2 C rco2(i) O1 oco
> end
>
> r1(1) = 0.400000 Ang
> r2(1) = 0.400001 Ang
> dr = 0.1 Ang
> do i = 1,19
> r1(i+1) = r1(i)
> r2(i+1) = r2(i) + dr
> enddo
>
> oco = 180 Deg
>
> basis = vqz                             ! Basis set specification
>
> do i = 1,20
>
> rco1(i) = r1(i)
> rco2(i) = r2(i)
>
> hf;
> enhf(i)=energy
>
> mp2;
> enmp2(i)=energy
>
> multi;
> emcscf(i) = energy
>
> enddo
>
> table rco1,rco2,enhf,enmp2,emcscf               !
> emscf          !,ecas,emrci
> save co2_mcscf.tab
> Title Results for CO2 (Angle = 180 Deg)
> !sort 3,1,2
> ---
>
> It produces the output but without convergence for the MCSCF
> calculations.
>
> Thank you in advance for any kind of help.
>
> regards
> Sunil
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--
Prof. Peter J. Knowles
School of Chemistry, Cardiff University, Main Building, Park Place,
Cardiff CF10 3AT, UK
Telephone: +44 29208 79182 Fax: +44 2920874030 Email KnowlesPJ at Cardiff.ac.uk