Computational study of the molecular ordering of vanadyl phthalocyanine monolayers on surfaces

The versatility of on-surface chemistry allows for designing a wide variety of molecule-based

quantum materials with properties tailored towards solid-state quantum devices, (1). In this work, we

explore molecular multilayers of metallo-phthalocyanine molecules as building block for such

quantum architectures. Vanadyl-phthalocyanine (VOPc) and the non-magnetic isostructural

Titanyl-phthalocyanine (TiOPc) are a prototypical realization which have been shown to exhibit

in long coherence times (T2) of the VOPc spin diluted in TiOPc, up to room temperature, (2-3).

Our focus lies on exploring strain engineering of TiOPc layers deposited on metal substrates to

create regular arrays of diluted VOPc multi-layers - akin to the strategy of VOPc diluted in TiOPc

powder - from first principles. The strain in the host layer creates a highly regular long-range

order without affecting the VOPc electronic structure. Based on our analysis, we anticipate that

the VOPc maintains its spin ½ character as well as the lifetime and coherence time. We furthe

highlight how shortcomings of the commonly employed generalized gradient approximation

(GGA) can be rectified by hybrid functionals and many-body perturbation theory (GW). We

present an accurate alignment between the molecular frontier orbitals and the silver states,

critical for the understanding of lack of charge transfer in this organic/metal interface.

Finally, we explore an extension of the 2-d architecture by vertical stacking of VOPc layers

which opens the door to exploit a third spatial dimension in the design of functional quantum

devices.

1. J. Am. Chem. Soc. 2019, 141, 29, 11339–11352

2. J. Am. Chem. Soc. 2016, 138, 7, 2154–2157

3. Nanoscale Horiz., 2019,4, 1202-1210