Gaussian 03 Online Manual
Last update: 2 October 2006


These method keywords request a Hartree-Fock calculation (RHF for singlets, UHF for higher multiplicities) followed by a Møller-Plesset correlation energy correction [60], truncated at second-order for MP2 [21,22,23,25,65], third order for MP3 [61,66], fourth-order for MP4 [62], and fifth-order for MP5 [64]. Analytic gradients are available for MP2 [22,23,139,140], MP3 and MP4(SDQ) [141,142], and analytic frequencies are available for MP2 [25].


There are four basic algorithms for MP2 calculations and for producing transformed (MO) integrals on disk:

  • Semi-Direct, which uses both main memory and external (disk) storage as available [23]. This is the default algorithm.

  • Direct, which uses no external storage by recomputing the integrals as needed during the       transformation.

  • Conventional, which stores the transformed integrals on disk. This was the only method       available in Gaussian 88, and the only method for generating MO integrals on disk in Gaussian 90. It is seldom a good choice on any but the smallest computer systems.

  • In-core, in which all the AO integrals are generated and stored in main memory, then used      without storing them externally.

The default is to decide between the in-core, direct, and semi-direct algorithms based on available memory and disk. The available disk can be specified via the MaxDisk keyword, either in the route section or (preferably) in the Default.Route file.

Note that selection of the direct or semi-direct MP2 and transformation algorithms is separate from selecting direct SCF (which is the default SCF algorithm in Gaussian 03). The E(2) calculation or transformation then recomputes integrals as needed in the form required for vectorization.


MP4(DQ) is specified to use only the space of double and quadruple substitutions, MP4(SDQ) for single, double and quadruple substitutions, or MP4(SDTQ) for full MP4 with single, double, triple and quadruple substitutions [62,63]. Just specifying MP4 defaults to MP4(SDTQ).


The MP5 code has been written for the open shell case only, and so specifying MP5 defaults to a UMP5 calculation. This method requires O3V3 disk storage and scales as O4V4 in cpu time.


The frozen-core options for defining inner-shells to be excluded from the correlation calculation are valid with these keywords. See the discussion here for details.


Note: The appropriate algorithm for MP2 will be selected automatically based on the settings of %Mem and MaxDisk. Thus, these options are almost never needed.

Forces the "fully direct" algorithm, which requires no external storage beyond that for the SCF. Requires a minimum of 2OVN words of main memory (O=number of occupied orbitals, V=number of virtual orbitals, N=number of basis functions). This is seldom a good choice, except for machines with very large main memory and limited disk.

Forces the semi-direct algorithm.

Requests some sort of direct algorithm. The choice between in-core, fully direct and semidirect is made by the program based on memory and disk limits and the dimensions of the problem.

Forces the in-memory algorithm. This is very fast when it can be used, but requires N4/4 words of memory. It is normally used in conjunction with SCF=InCore. NoInCore prevents the use of the in-core algorithm.

MP2: Energies, analytic gradients, and analytic frequencies. ROMP2 is available for energies only.

MP3, MP4(DQ) and MP4(SDQ): Energies, analytic gradients, and numerical frequencies.

MP4(SDTQ) and MP5: Analytic energies, numerical gradients, and numerical frequencies.

HF, SCF, Transformation, MaxDisk

Energies. The MP2 energy appears in the output as follows, labeled as EUMP2:

E2=     -.3906492545D-01 EUMP2=     -.75003727493390D+02 

Energies for higher-order Møller-Plesset methods follow. Here is the output from an MP4(SDTQ) calculation:

Time for triples=          .04 seconds. 
MP4(T)=     -.55601167D-04 
E3=         -.10847902D-01      EUMP3=         -.75014575395D+02 
E4(DQ)=     -.32068082D-02      UMP4(DQ)=      -.75017782203D+02 
E4(SDQ)=    -.33238377D-02      UMP4(SDQ)=     -.75017899233D+02 
E4(SDTQ)=   -.33794389D-02      UMP4(SDTQ)=    -.75017954834D+02 

The energy labelled EUMP3 is the MP3 energy, and the various MP4-level corrections appear after it, with the MP4(SDTQ) output coming in the final line (labeled UMP4(SDTQ)).