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Re^2: 'Abnormal Energy' obtained in MP4 single point energy calculation


Dear Xaiza,

I took a closer look at the COORD=CART vs COORD=UNIQUE results. Below are the full results I got with COORD=UNIQUE.

            E(RHF)       =      -309.9452940189

            E(D,2)       =        -1.1633058478
            E(MP2)       =      -311.1085998668

            E(D,3)       =        -0.0646773525
            E(D,2+3)     =        -1.2279832003
            E(MP3)       =      -311.1732772192

            E(S,4)       =        -0.0103910437
            E(D,4)       =        -0.0305512257
            E(D,2+3+4)   =        -1.2585344260
            E(R+Q,4)     =         0.0296010672
            E(SDQ,4)     =        -0.0113412021
            E(SDQ,2+3+4) =        -1.2393244024
            E(MP4-SDQ)   =      -311.1846184214

If I compare them with the COORD=CART results, I find that not only the MP4 energy is different. The MP2 and MP3 energies also differ, though these differences are much smaller (3.6 kJ/mol at the MP2 level). Because of these small differences, the COORD=CART results thus might not look suspicious at first glance. If you have performed more calculations with COORD=CART, I would advise you to take a second look at them to see if these exhibit the same problem.

Kind regards,

On Wed Jun 26 '13 4:57pm, Thomas wrote
>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 5:13pm by the author ]

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