[molpro-user] Changing the convergence threshold for FCI calculation

[Peter Knowles]

Sorry about this missing documentation for fci. Here is what you can say:

fci
davidson,sym,trial,result,maxit,thresh,rhs,shift,threshresult,ioption,nroot

If you omit any parameter, the default is taken; the convergence 
threshold is 'thresh'

Peter

Bastiaan J. Braams wrote:
>I would like advice about how to modify the convergence threshold for
>an FCI calculation.  I am working on the CH2 molecule, and when using
>the vtz or avtz basis all calculations fail.  When using the vdz basis
>I obtain answers, but I can see that the calculation iterates many
>times beyond a result that would satisfy me.
>
>Here is a sample input.
>
>***,SP ENERGY FOR H2C1 singlet
>memory,84,m
>punch,mpsp.pun,new
>geomtyp=xyz
>geometry
>z;mass
> 3
>  null
> H      0.32378690   1.07256700   0.23934060
> H     -1.09156370   0.02483350  -0.31998320
> C      0.06398140   0.01112250   0.00672000
>end
>basis=vdz
>rhf;wf,charge=0,sym=1,spin=0
>fci
>---
>
>A fragment of output follows (terminated by -----------------------)
>
>[...]
>
>1PROGRAM * FCI (Full CI)     Author: P.J. Knowles, 1984
>
>[...]
>
> Symmetry:                   1
> Trial vector:                  0.00
> Result vector:                 0.00
> Maximum iterations:           35
> Convergence threshold:         0.0000100
> RHS vector:                    0.00
> Hamiltonian shift:             0.0000000
> Output threshold:              0.0500000
> Options:                        0
> Number of roots:             1
>
>[...]
>
>0Hamiltonian diagonaliser entered at time      0.28
>0Initial configuration generated:
>       1      1.0000000    -38.8759613
>
> It  Tr    CPU  Convergence   Energy       Pop     dE(next)
>
>  1   1   65.6  1.00000000   -38.87596134
>+                                         0.00 -0.15591787 -0.15590860
>  2   1  126.4  0.26533724   -39.00592383
>+                                         0.03 -0.01455227 -0.01428755
>  3   1  198.4  0.07323397   -39.01771922
>+                                         0.07 -0.00216144 -0.00207235
>  4   1  282.3  0.04111007   -39.01957171
>+                                         0.10 -0.00041959 -0.00038686
>  5   1  375.7  0.01436230   -39.01998285
>+                                         0.14 -0.00010137 -0.00009012
>  6   1  480.7  0.00973387   -39.02008870
>+                                         0.18 -0.00003209 -0.00002752
>  7   1  597.4  0.00433518   -39.02012031
>+                                         0.23 -0.00001094 -0.00000938
>  8   1  725.6  0.00232195   -39.02013078
>+                                         0.26 -0.00000321 -0.00000274
>  9   1  862.9  0.00113916   -39.02013371
>+                                         0.27 -0.00000084 -0.00000072
> 10   1 1003.4  0.00049931   -39.02013447
>+                                         0.27 -0.00000021 -0.00000018
> 11   1 1142.4  0.00027325   -39.02013466
>+                                         0.27 -0.00000005 -0.00000004
> 12   1 1282.3  0.00012684   -39.02013470
>+                                         0.27 -0.00000001 -0.00000001
> 13   1 1421.8  0.00006938   -39.02013471
>+                                         0.27  0.00000000  0.00000000
> 14   1 1562.8  0.00003321   -39.02013472
>+                                         0.28  0.00000000  0.00000000
> 15   1 1705.6  0.00001761   -39.02013472
>+                                         0.28  0.00000000  0.00000000
> 16   1 1847.5  0.00000788   -39.02013472
>
>-----------------------
>
>As I said, this was on a vdz basis, and on a vtz basis it never
>reaches its tolerance limits.  I would be happy to see the calculation
>stop when the energy change is below 1.0e-6, or even 1.0e-5.
>
>Presumably the relevant parameter is the "convergence threshold",
>which is 1.0e-5 according to the output.  So how do I change this
>parameter?  I tried to insert the command
>
>gthresh,civec=1.d-2
>
>before my geometry specification, but this had no effect.
>
>Bas Braams
>--
>Bastiaan J. Braams
>braams at mathcs.emory.edu
>Emory University, Atlanta, GA
>  

-- 
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  WWW http://www.cardiff.ac.uk/chemy/staff/knowles.html