Xuanyuan

Xuanyuan is used to calculate one electron and two electron integrals. It is named after Chinese ancestor Xuanyuan Huangdi.

General keywords

Direct

Ask for integral direct calculations. It is default now but may be turned off by the keyword Saorb in Compass.

Nondirect

When the Skeleton Fock matrix is used, ask for non-direct calculation for Fock matrix. The integrals, such as two-electron repulsive integrals, 3-center RI integrals are calculated saved. If Saorb is used in COMPASS, nondirect is the default.

Skipint

This keyword only works with direct-SCF and the LSSCF module. It asks for skip 2-electron K2 integrals used in Schwartz prescreening. The K2 integrals will be calculated in LSSCF.

Maxmem

Set maximum memory used in the integral calculation. This keyword works with Saorb in COMPASS. The unit can be MW and GW, i.e. Mega Words and Giga Words

Examples:

$xuanyuan
Maxmem
  512MW
$end

RSOMEGA / RS

Range separation ERIs required. RS is a synonym for RSOMEGA. No default value. Suggested value: 0.33.

Examples:

$xuanyuan
Rsomega
 0.33
$end

Heff

Heff is a keyword to turn on scalar relativistic effects using sf-X2C (Heff=3) by default

Other options for Heff are

0, nonrelativistic, including the cases of scalar ECP and SOECP

1, sf-ZORA

2, sf-IORA

3/4, sf-X2C

5, sf-X2C+so-DKH3 (spin-free)

21, sf-X2C

22, sf-X2C with atom-block-diagonal X and full R (sf-X2C-aXR) [ZouLiu2020]

23, sf-X2C with atom-block-diagonal unitary transformation (sf-X2C-aU) [ZouLiu2020]

Among these relativistic Hamiltonians, 21, 22, and 23 have analytic gradients, hessians, and some one-electron properties (Mossbauer spectroscopy related properties at present in scf).

Example:

$xuanyuan
heff
3
$end

Hsoc

Hsoc is a keyword to turn on soc integral calculations in post-SCF steps. Default option for hsoc is 0 (only 1e-soc int). The recommended option is 2 (so1e+somf2e). In the case of ECP (including mixed ECP, SOECP, and all-electron N.R. basis sets), only 10 (BP so-1e) is acceptable, i.e. SOECP integrals for SOECP atoms whereas effective nuclear charges for ECP and all-electron atoms.

Other options are used in soint_util/somf2e.F90 for choosing different combinations of so1e and mean-feild so2e (SOMF) operators.

0 so-1e

1 so-1e + somf (two-electron spin-orbit interaction is included via an effective fock operator)

2 so1e + somf-1c (one-center approximation to two-electron integrals)

3 so-1e + somf-1c / no soo (turn off spin-other-orbit contributions)

4 so-1e + somf-1c / no soo + WSO_XC (use dft xc functional as soo part)

5 so-1e + somf-1c / no soo + WSO_XC(-2x: following Neese's paper scale dft part by -2 to mimic soo part)

These options plus 10 gives the operators in BP approximations. In practice, hsoc=1 is the most accurate, and hsoc=2 is preferred for large molecules.

Note if heff=5, then the one-electron part will be calculated in xuanyuan and stored in disc for so-DKH3 type one-electron spin-orbit term. The accuracy of such an operator requires further tests.

Examples:

$xuanyuan
heff
3
hsoc
2
$end

Nuclear

Nuclear defines the nuclear charge distribution used in the V and pVp integrals in all-electron relativistic calculations, which can be -1 for point charge model (debug only), 0 for point charge model (default), 1 for finite nucleus model by an s-type Gaussian function, and other finite nucleus models (N.Y.I.). In the case of contracted Gaussian basis sets with a finite nucleus model (e.g. ANO-R and ANO-R-n, n = 0, 1, 2, 3), 1 must be used.

For Za < 110, the nuclear charge radii are taken from Ref.[Visscher1997] (in a.u).

For Za ≥ 110, the nuclear charge radius is 0.57 + 0.836 * A^1/3 (in fm), where the isotope mass number A is estimated by Za according to the relationship A(Za) = 0.004467 * Za² + 2.163 * Za - 1.168. See Appendix A in Ref.[Andrae2000] and Ref.[Andrae2002].

NOTE: the finite nucleus model has been implemented only in scalar calculations at present, but will be used in SOC calculations soon.

Cholesky

• The following line contains a string and a float number. Set method and threshold of ERI Cholesky decomposition. S-CD for standard CD. 1c-CD for one center Cholesky decomposition.

Examples:

$xuanyuan
Cholesky
  S-CD 1.d-5
$end

Expert keywords

NoCheck

For Heff=21 only: check inverse variational collapse (IVC; see Ref.[Liu2007]). Stop (0; default) or not (1) in the case of IVC.

IVC may lead to numerical instability, which may be serious in geometry optimization.

NRDebug

In relativistic calculations, use a C-light of 10^8 to reproduce non-relativistic results (for debug only).

Keyword3

xxx

Keyword4

xxx

Depend Files

Examples

N.A.

References

• [Andrae2000] D. Andrae, Phys. Rep. 336, 413 (2000).
• [Andrae2002] D. Andrae, Nuclear charge density distributions in quantum chemistry, in Relativistic Electronic Structure Theory, Part 1: Fundamentals, P. Schwerdtfeger Ed., Theoretical and Computational Chemistry, Vol. 11, Elsevier, 2002.
• [Liu2007] W. Liu and W. Kutzelnigg, J. Chem. Phys. 126, 114107 (2007).
• [Visscher1997] L. Visscher and K. G. Dyall, At. Data and Nucl. Data Tables 67, 207 (1997).

• [ZouLiu2020] W. Zou, G. Guo, B. Suo, and W. Liu, J. Chem. Theory Comput. 16, 1541 (2020).