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Re: 'Abnormal Energy' obtained in MP4 single point energy calculation


Dear Xaiza,

I tested your job and was able to get correct energies by specifying COORD=UNIQUE instead of COORD=CART. COORD=CART should almost never be used.

With COORD=CART: E(MP4-SDQ)   =      -416.5578285615

With COORD=UNIQUE: E(MP4-SDQ)   =      -311.1846184214

In addition, as Pedro already pointed out, you should use tighter accuracy settings when you have a partial linear dependence in your basis set. I tested with the following settings:


and got the following value:

E(MP4-SDQ)   =      -311.1842023882

That's a 1 kJ/mol difference compared to the second result above.

Kind regards,

PS Note that above results are without the T part as this made troubleshooting faster.

On Wed Jun 26 '13 2:49pm, Xaiza wrote
>Hello everyone!

>I am currently running an MP4 single point energy calculation (basis set: 6-311++G**) on a few hydrocarbons using Firefly version 7.1.G in one of the PCs in our laboratory. The geometry I used for the single point energy calculation was the equilibrium geometry I obtained from my MP2 optimization calculation using the same molecule. On some of my molecules examined at MP4, I found out that the energy calculated was 'abnormally' large(i.e. the absolute value of the energy calculated) that my succeeding calculations (i.e. enthalpy of reaction, enthalpy of activation, etc. ) doesn't make any sense at all. I checked my input files, they were all the same. I just changed the geometry. Shown below is the fraction of my result wherein the energy I label as 'abnormal' is reflected.


>            E(RHF)       =      -309.9452940908

>            E(D,2)       =        -1.1646736559
>            E(MP2)       =      -311.1099677467

>            E(D,3)       =        -0.0698223432
>            E(D,2+3)     =        -1.2344959991
>            E(MP3)       =      -311.1797900899

>            E(S,4)       =        -0.0443751557
>            E(D,4)       =      -105.3701897285
>            E(D,2+3+4)   =      -106.6046857276
>            E(T,4)       =        -0.0706244480
>            E(R+Q,4)     =         0.0297425817
>            E(SDTQ,4)    =      -105.4554467506
>            E(SDTQ,2+3+4)=      -106.6899427497
>            E(MP4-SDTQ)  =      -416.6352368404

> ..... DONE WITH MP4 ENERGY .....

>  I also attached the output file of this calculation. What might be the problem in this calculation? Can I ask for suggestions on how to improve/solve such? Any help is highly appreciated. Thank you in advance!

[ This message was edited on Wed Jun 26 '13 at 4:57pm by the author ]

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