#include <CASPT2.h>

Public Member Functions
	CASPT2 (DMRGSCFindices idx, DMRGSCFintegrals ints, DMRGSCFmatrix oei, DMRGSCFmatrix fock, double one_dm, double two_dm, double three_dm, double contract, const double IPEA)
	Constructor. More...

virtual	~CASPT2 ()
	Destructor.

double	solve (const double imag_shift, const bool CONJUGATE_GRADIENT=false) const
	Solve for the CASPT2 energy (note that the IPEA shift has been set in the constructor) More...

Static Public Member Functions
static long long	vector_length (const DMRGSCFindices *idx)
	Return the vector length for the CASPT2 first order wavefunction (before diagonalization of the overlap matrix) More...

Detailed Description

CASPT2 class.

Author: Sebastian Wouters sebas.nosp@m.tian.nosp@m.woute.nosp@m.rs@g.nosp@m.mail..nosp@m.com

Date: December 11, 2015

Information

The CASPT2 class contains the functions to perform second order multireference perturbation theory on top of a CASSCF wavefuntion [CASPT1, CASPT2]. CASPT2 has recently also been used with DMRG as active space solver: the active space 4-RDM contracted with the Fock operator, together with the 1-, 2- and 3-RDM are required thereto [CASPT3]. Alternatively, cumulant approximations can be used as well [CASPT4]. To mitigate problems with CASPT2 several modifications of the zeroth order Hamiltonian have been introduced: IPEA corrections [CASPT5], the g1 term [CASPT6], real level shifts [CASPT7] and imaginary level shifts [CASPT8].

References

[CASPT1] K. Andersson, P.-A. Malmqvist, B.O. Roos, A.J. Sadlej and K. Wolinski, Journal of Physical Chemistry 94, 5483-5488 (1990). http://dx.doi.org/10.1021/j100377a012
[CASPT2] K. Andersson, P.‐A. Malmqvist and B.O. Roos, Journal of Chemical Physics 96, 1218-1226 (1992). http://dx.doi.org/10.1063/1.462209
[CASPT3] Y. Kurashige and T. Yanai, Journal of Chemical Physics 135, 094104 (2011). http://dx.doi.org/10.1063/1.3629454
[CASPT4] Y. Kurashige, J. Chalupsky, T.N. Lan and T. Yanai, Journal of Chemical Physics 141, 174111 (2014). http://dx.doi.org/10.1063/1.4900878
[CASPT5] G. Ghigo, B.O. Roos and P.-A. Malmqvist, Chemical Physics Letters 396, 142-149 (2004). http://dx.doi.org/10.1016/j.cplett.2004.08.032
[CASPT6] K. Andersson, Theoretica Chimica Acta 91, 31-46 (1995). http://dx.doi.org/10.1007/BF01113860
[CASPT7] B.O. Roos and K. Andersson, Chemical Physics Letters 245, 215-223 (1995). http://dx.doi.org/10.1016/0009-2614(95)01010-7
[CASPT8] N. Forsberg and P.-A. Malmqvist, Chemical Physics Letters 274, 196-204 (1997). http://dx.doi.org/10.1016/S0009-2614(97)00669-6

Definition at line 62 of file CASPT2.h.

Constructor & Destructor Documentation

CheMPS2::CASPT2::CASPT2	(	DMRGSCFindices *	idx,
		DMRGSCFintegrals *	ints,
		DMRGSCFmatrix *	oei,
		DMRGSCFmatrix *	fock,
		double *	one_dm,
		double *	two_dm,
		double *	three_dm,
		double *	contract,
		const double	IPEA
	)

Constructor.

Parameters

idx	DMRGSCFindices which contain the partitioning into occupied, active, and virtual orbitals per irrep
ints	The two-electron integrals needed for CASSCF and CASPT2, in pseudocanonical orbitals
oei	All one-electron integrals, in pseudocanonical orbitals
fock	The fock matrix of CASPT2, in pseudocanonical orbitals
one_dm	The spin-summed one-particle density matrix one_dm[i+L*j] = sum_sigma < a^+_i,sigma a_j,sigma > (with L the number DMRG orbitals), in pseudocanonical orbitals
two_dm	The spin-summed two-particle density matrix two_dm[i+L(j+L(k+L*l))] = sum_sigma,tau < a^+_i,sigma a^+_j,tau a_l,tau a_k,sigma > (with L the number DMRG orbitals), in pseudocanonical orbitals
three_dm	The spin-summed three-particle density matrix three_dm[i+L(j+L(k+L(l+L(m+L*n))))] = sum_z,tau,s < a^+_{i,z} a^+_{j,tau} a^+_{k,s} a_{n,s} a_{m,tau} a_{l,z} > (with L the number DMRG orbitals), in pseudocanonical orbitals
contract	The spin-summed four-particle density matrix contracted with the fock operator contract[i+L(j+L(k+L(p+L(q+L*r))))] = sum_{t,sigma,tau,s} fock(t,t) < a^+_{i,sigma} a^+_{j,tau} a^+_{k,s} E_{tt} a_{r,s} a_{q,tau} a_{p,sigma} > (with L the number DMRG orbitals), in pseudocanonical orbitals
IPEA	The CASPT2 IPEA shift from Ghigo, Roos and Malmqvist, Chemical Physics Letters 396, 142-149 (2004)

Definition at line 39 of file CASPT2.cpp.

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Member Function Documentation

double CheMPS2::CASPT2::solve	(	const double	imag_shift,
		const bool	CONJUGATE_GRADIENT = `false`
	)		const

Solve for the CASPT2 energy (note that the IPEA shift has been set in the constructor)

Parameters

imag_shift	The CASPT2 imaginary shift from Forsberg and Malmqvist, Chemical Physics Letters 274, 196-204 (1997)
CONJUGATE_GRADIENT	If true (false), the conjugate gradient (Davidson) algorithm is used to solve the CASPT2 equation