Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids <i>κ</i>-(BEDT-TTF)₂<i>X</i>

• Main Authors: Predrag Lazić, Ognjen Milat, Branko Gumhalter, Silvia Tomić
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Crystals
• Subjects: mott insulators; quantum spin liquid; strongly correlated systems; density functional theory
• Online Access: https://www.mdpi.com/2073-4352/9/7/348

Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as <inline-formula> <math display="inline"> <semantics> <mi>&#954;</mi> </semantics> </math> </inline-formula>-(BEDT-TTF)<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mrow></mrow> <mn>2</mn> </msub> <mi>X</mi> </mrow> </semantics> </math> </inline-formula>. Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, <inline-formula> <math display="inline"> <semantics> <mi>&#954;</mi> </semantics> </math> </inline-formula>-(BEDT-TTF)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>Cu<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>(CN)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>, <inline-formula> <math display="inline"> <semantics> <mi>&#954;</mi> </semantics> </math> </inline-formula>-(BEDT-TTF)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>Ag<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>(CN)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>3</mn> </msub> </semantics> </math> </inline-formula>, and <inline-formula> <math display="inline"> <semantics> <mi>&#954;</mi> </semantics> </math> </inline-formula>-(BEDT-TTF)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>Cu[N(CN)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system <inline-formula> <math display="inline"> <semantics> <mi>&#954;</mi> </semantics> </math> </inline-formula>-(BEDT-TTF)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>Cu[N(CN)<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>2</mn> </msub> </semantics> </math> </inline-formula>]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results.