Capabilities and Alternate Implementations

Depending on the reference (e.g., RHF, UHF, ROHF), the integral treatment (conventional CONV, density-fitted DF, and Cholesky-decomposed CD), active orbitals, and derivative level, computational methods are sometimes assembled from implementations by multiple coders. Conversely, some capabilities may be implemented multiple times. Capabilities, modules, algorithm types, and defaults are detailed for many ground-state methods at Table Module Capabilities. Its analogous summary table (with modules collapsed) is at Summary Capabilities. PSI4 transparently selects the most efficient implementation, so one generally needn’t consult this table. However, to understand the details of what combinations are accessible or what alternate implementations are available, read on.

Note that HF, DFT, and MPn (n<=3) default to density-fitted integrals, while all higher methods default to conventional integrals. Therefore, for a closed-shell molecule:

# runs MP2 with default algorithm type ``DF`` with default implementation DFMP2
energy('mp2')

# runs MP2 with algorithm type ``CONV`` with default implementation OCC
set mp2_type conv
energy('mp2')

# runs MP2 with default algorithm type ``DF`` with implementation OCC
set qc_module occ
energy('mp2')

# runs MP2 with algorithm type ``CONV`` with implementation FNOCC
set mp2_type conv
set qc_module fnocc
energy('mp2')

Capabilities of PSI4, including details of overlapping modules. “✓” runs analytically. “∷” runs derivative with internal finite difference. Single underline “✓̲” or “∷̲” is default module when QC_MODULE unspecified. Double underline “✓̳” or “∷̳” is default algorithm type when type selector (e.g., CC_TYPE) unspecified.

◻ ◻ name ↓ → type[1] ↓ → ◻	QC_MODULE ↓ REFERENCE → ◻ ◻ FREEZE_CORE[2]→	PSI4 Capabilities
		Restricted (RHF)												Unrestricted (UHF)												Restricted Open (ROHF)
		energy()						gradient()[3]						energy()						gradient()[3]						energy()						gradient()[3]
		CV		DF		CD		CV		DF		CD		CV		DF		CD		CV		DF		CD		CV		DF		CD		CV		DF		CD
		A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F	A	F
hf SCF_TYPE		✓		✓̳		✓		✓		✓̳		∷		✓		✓̳		✓		✓		✓̳		∷		✓		✓̳		✓		✓		✓̳		∷
	SCF	✓̲		✓̳		✓̲		✓̲		✓̳				✓̲		✓̳		✓̲		✓̲		✓̳				✓̲		✓̳		✓̲		✓̲		✓̳
mp2 MP2_TYPE		✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷	✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷	✓	✓	✓̳	✓̳	✓	✓	∷	∷	∷̳	∷̳	∷	∷
	DETCI	✓	✓
	DFMP2[4]			✓̳	✓̳					✓̳	✓̳					✓̳	✓̳											✓̳	✓̳
	FNOCC	✓	✓
	OCC	✓̲	✓̲	✓	✓	✓̲	✓̲	✓̲		✓	✓			✓̲	✓̲	✓	✓	✓̲	✓̲	✓̲		✓̳	✓̳			✓̲	✓̲	✓	✓	✓̲	✓̲
mp2.5 MP_TYPE		✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷	✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷
	OCC	✓̲	✓̲	✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳			✓̲	✓̲	✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳
mp3 MP_TYPE		✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷	✓	✓	✓̳	✓̳	✓	✓	✓	∷	✓̳	✓̳	∷	∷
	DETCI	✓	✓
	FNOCC	✓	✓
	OCC	✓̲	✓̲	✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳			✓̲	✓̲	✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳
mp4(sdq) MP_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
mp4, mpn[5] MP_TYPE		✓̳	✓̳
	DETCI	✓	✓
	FNOCC	✓̳	✓̳
zapt2, zaptn[5] MP_TYPE																										✓̳	✓̳
	DETCI																									✓̳	✓̳
cisd, cin[5] CI_TYPE		✓̳	✓̳																							✓̳	✓̳
	DETCI	✓	✓																							✓̳	✓̳
	FNOCC	✓̳	✓̳
qcisd CI_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
qcisd(t) CI_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
fci CI_TYPE		✓̳	✓̳																							✓̳	✓̳
	DETCI	✓̳	✓̳																							✓̳	✓̳
remp2 CC_TYPE		✓̳	✓̳	✓	✓	✓	✓							✓̳	✓̳	✓	✓	✓	✓
	OCC	✓̳	✓̳	✓̲	✓̲	✓̲	✓̲							✓̳	✓̳	✓̲	✓̲	✓̲	✓̲
lccd CC_TYPE		✓̳	✓̳	✓	✓	✓	✓	✓̳	∷̳	✓	✓	∷	∷	✓̳	✓̳	✓	✓	✓	✓	✓̳	∷̳	✓	✓	∷	∷
	FNOCC	✓̳	✓̳
	OCC	✓	✓	✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳	✓̳	✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲
lccsd, cepa(0) CC_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
cepa(1) CC_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
cepa(3) CC_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
acpf CC_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
aqcc CC_TYPE		✓̳	✓̳
	FNOCC	✓̳	✓̳
ccd CC_TYPE				✓	✓	✓	✓			✓	✓	∷	∷			✓	✓	✓	✓			✓	✓	∷	∷
	OCC			✓̲	✓̲	✓̲	✓̲			✓̲	✓̲					✓̲	✓̲	✓̲	✓̲			✓̲	✓̲
bccd CC_TYPE		✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
	CCENERGY	✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
cc2 CC_TYPE		✓̳	✓̳					✓̳	∷̳					✓̳	✓̳					∷̳	∷̳					✓̳	✓̳					∷̳	∷̳
	CCENERGY	✓̳	✓̳					✓̳						✓̳	✓̳											✓̳	✓̳
ccsd CC_TYPE		✓̳	✓̳	✓	✓	✓	✓	✓̳	∷̳	✓	✓	∷	∷	✓̳	✓̳	✓	✓	✓	✓	✓̳	∷̳	✓	✓	∷	∷	✓̳	✓̳					✓̳	∷̳
	CCENERGY	✓̳	✓̳					✓̳						✓̳	✓̳					✓̳						✓̳	✓̳					✓̳
	FNOCC	✓	✓	✓̲	✓̲	✓̲	✓̲
	MRCC	✓	✓											✓	✓											✓	✓
	OCC			✓	✓	✓	✓			✓̲	✓̲					✓̲	✓̲	✓̲	✓̲			✓̲	✓̲
ccsd(t) CC_TYPE		✓̳	✓̳	✓	✓	✓	✓	✓̳	∷̳	✓	✓	∷	∷	✓̳	✓̳					✓̳	∷̳					✓̳	✓̳					∷̳	∷̳
	CCENERGY	✓̳	✓̳					✓̳						✓̳	✓̳					✓̳						✓̳	✓̳
	FNOCC	✓	✓	✓̲	✓̲	✓̲	✓̲
	MRCC	✓	✓											✓	✓											✓	✓
	OCC			✓	✓	✓	✓			✓̲	✓̲
a-ccsd(t)[6] CC_TYPE		✓̳	✓̳	✓	✓	✓	✓
	CCENERGY	✓̳	✓̳
	MRCC	✓	✓											✓	✓											✓	✓
	OCC			✓̲	✓̲	✓̲	✓̲
bccd(t) CC_TYPE		✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
	CCENERGY	✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
cc3 CC_TYPE		✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
	CCENERGY	✓̳	✓̳											✓̳	✓̳											✓̳	✓̳
	MRCC	✓	✓											✓	✓
omp2 MP2_TYPE		✓		✓̳	✓̳	✓	✓	✓		✓̳	✓̳	∷	∷	✓		✓̳	✓̳	✓	✓	✓		✓̳	✓̳	∷	∷	✓		✓̳	✓̳	✓	✓	✓		✓̳	✓̳	∷	∷
	OCC[4]	✓̲		✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳			✓̲		✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳			✓̲		✓̳	✓̳	✓̲	✓̲	✓̲		✓̳	✓̳
omp2.5 MP_TYPE		✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷
	OCC[4]	✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲
omp3 MP_TYPE		✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷
	OCC[4]	✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲
oremp2 CC_TYPE		✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷
	OCC[4]	✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲
olccd CC_TYPE		✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷	✓̳		✓	✓	✓	✓	✓̳		✓	✓	∷	∷
	OCC[4]	✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲			✓̳		✓̲	✓̲	✓̲	✓̲	✓̳		✓̲	✓̲
svwn, LSDA DFT SCF_TYPE		✓		✓̳		✓		✓		✓̳		∷		✓		✓̳		✓		✓		✓̳		∷
	SCF	✓̲		✓̳		✓̲		✓̲		✓̳				✓̲		✓̳		✓̲		✓̲		✓̳
pbe, GGA DFT SCF_TYPE		✓		✓̳		✓		✓		✓̳		∷		✓		✓̳		✓		✓		✓̳		∷
	SCF	✓̲		✓̳		✓̲		✓̲		✓̳				✓̲		✓̳		✓̲		✓̲		✓̳
b3lyp, Hybrid DFT SCF_TYPE		✓		✓̳		✓		✓		✓̳		∷		✓		✓̳		✓		✓		✓̳		∷
	SCF	✓̲		✓̳		✓̲		✓̲		✓̳				✓̲		✓̳		✓̲		✓̲		✓̳
wb97x, LRC DFT SCF_TYPE		✓		✓̳				✓		✓̳				✓		✓̳				✓		✓̳
	SCF	✓̲		✓̳				✓̲		✓̳				✓̲		✓̳				✓̲		✓̳
b2plyp, DH DFT[7] SCF_TYPE		✓	✓	✓̳	✓̳	✓	✓							✓	✓	✓̳	✓̳	✓	✓
	SCF	✓̲	✓̲	✓̳	✓̳	✓̲	✓̲							✓̲	✓̲	✓̳	✓̳	✓̲	✓̲

[1]

Algorithm type selection keyword below. Values to the right: conventional CV, density-fitted DF, and Cholesky-decomposed CD.

[2]

Active orbital values to the right: all-electron A and frozen-core F.

[3] (1,2,3)

Finite difference gradients are only marked explicitly by “∷” for overall (not per-method) lines and when at least one case has analytic gradients implemented, but the capability can be gleaned from the energy availability.

[4] (1,2,3,4,5,6)

Also available for DFT references RKS/UKS

[5] (1,2,3)

Arbitrary-order n through DETCI is inefficient byproduct of CI

[6]

a-CCSD(T) also known as CCSD(aT), Lambda-CCSD(T), and CCSD(T)_L

[7]

DH-DFT only available with DF-MP2