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
>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:
>$CONTRL ICUT=11 INTTYP=HONDO $END
>$SCF CONV=7 $END
>and got the following value:
>E(MP4-SDQ) = -311.1842023882
>That's a 1 kJ/mol difference compared to the second result above.
>PS Note that above results are without the T part as this made troubleshooting faster.
>On Wed Jun 26 '13 2:49pm, Xaiza wrote
>>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.
>> RESULTS OF MOLLER-PLESSET 4TH ORDER CORRECTION ARE
>> 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 ]