## 1 Introduction  
Polymorphisms, defined as the property of a substance to manifest in two or more crystalline phases with distinct molecular arrangements or conformations in the crystal lattice, are a phenomenon of significant relevance in applied sciences [1, 2, 3]. Molecular-level changes among polymorphs can result in distinct properties, including hygroscopicity, solubility, thermal stability, release rate, hardness, and chemical reactivity [4]. Since its inception, chemistry has predominantly utilised temperature to generate or alter materials; nevertheless, the application of pressure above a few tens of atmospheres for similar reasons has been infrequently recorded. The application of high pressure has demonstrated efficacy in uncovering fresh states in solid-state materials, exemplified by the transformation of graphite into diamond [5]. Under increased pressure, the organisation of both inter- and intramolecular contacts can often be altered, new hydrogen bonds can form, and existing ones can be broken or symmetrized. Pressure-induced phase transitions often manifest in one of three forms: a direct transition between higher- and lower-symmetry space groups (type I), a transition including a low-symmetry state linking higher-symmetry initial and final structures (type II), or a more complex transformation process (type III). Isosymmetric structural phase transitions (IPT, type 0), characterised by the absence of alterations in the occupation of Wyckoff positions, the atom count in the unit cell, and the space group symmetry, are rather rare [6]. Nonetheless, there exist several notable and newly identified instances of such transitions; sodium oxalate [7], 1,3-cyclohexanedione [8], L-serine [9], chlorothiazide [10], biurea [11], and glycylglycine [12] are just some of the well-known examples. Density functional theory (DFT) methods are frequently applied to model the structure and properties of organic materials and compounds. The distinctiveness of each polymorphic form primarily arises from both short- and long-range intermolecular interactions. Consequently, DFT-based approaches modelling a single molecule in vacuum or solution were deemed insufficient and imprecise for investigating polymorphism-related events. Although \"single molecule\" methods are typically effective in various areas of sciences, such as investigating drug-biomolecule interactions or predicting complex formation, the study on molecular crystals necessitated the use of alternative calculations, often referred to as \"periodic DFT calculations\" [13]. The term \"periodic\" abbreviates \"performed under periodic boundary conditions\", a critical prerequisite for precise crystal modelling. Moreover, in these computations, pseudopotentials are commonly employed to depict an effective interaction that approximates the potential encountered by valence electrons. Furthermore, plane wave-basis sets are usually utilised in lieu of localised ones. Sulfamic acid (SA) is the derivative of sulfuric acid and serves as a model for investigating the properties of hydrogen-bonded molecular crystals under severe circumstances. This classical chemical is extensively utilised in industry and has garnered significant interest owing to its broad applications and distinctive features. For example, it is an acidic cleaning agent and can be utilised as a component in the production of flameproof materials [14]. Simultaneously, the steady characteristics of SA render it a standard substance for nonaqueous titrimetric analysis [15]. The most renowned application of SA is its role as a catalyst for swift and highly efficient synthesis [16]. It is important to acknowledge that SA exists as a zwitterion, NH3+SO3-, in the solid state under ambient conditions. The zwitterionic characteristic of SA not only results in distinctive physical qualities, such as a high melting point of around 205 \({}^{\circ}\)C, unlike other sulfonic acids, but also enables it to function as a recyclable catalyst, which may be reused via straightforward filtration and washing.